IterTools - PHP Iteration Tools to Power Up Your Loops

Inspired by Python—designed for PHP.

Features

IterTools makes you an iteration superstar by providing two types of tools:

Loop iteration tools
Stream iteration tools

Loop Iteration Tools Example

foreach (Multi::zip(['a', 'b'], [1, 2]) as [$letter, $number]) {
    print($letter . $number);  // a1, b2
}

Stream Iteration Tools Example

$result = Stream::of([1, 1, 2, 2, 3, 4, 5])
    ->distinct()                 // [1, 2, 3, 4, 5]
    ->map(fn ($x) => $x**2)      // [1, 4, 9, 16, 25]
    ->filter(fn ($x) => $x < 10) // [1, 4, 9]
    ->toSum();                   // 14

All functions work on iterable collections:

array (type)
Generator (type)
Iterator (interface)
Traversable (interface)

README docs translated in other languages:

Русский

Quick Reference

Loop Iteration Tools

Multi Iteration

Iterator	Description	Code Snippet
`chain`	Chain multiple iterables together	`Multi::chain($list1, $list2)`
`zip`	Iterate multiple collections simultaneously until the shortest iterator completes	`Multi::zip($list1, $list2)`
`zipEqual`	Iterate multiple collections of equal length simultaneously, error if lengths not equal	`Multi::zipEqual($list1, $list2)`
`zipFilled`	Iterate multiple collections, using a filler value if lengths not equal	`Multi::zipFilled($default, $list1, $list2)`
`zipLongest`	Iterate multiple collections simultaneously until the longest iterator completes	`Multi::zipLongest($list1, $list2)`

Single Iteration

Iterator	Description	Code Snippet
`chunkwise`	Iterate by chunks	`Single::chunkwise($data, $chunkSize)`
`chunkwiseOverlap`	Iterate by overlapped chunks	`Single::chunkwiseOverlap($data, $chunkSize, $overlapSize)`
`compress`	Filter out elements not selected	`Single::compress($data, $selectors)`
`compressAssociative`	Filter out elements by keys not selected	`Single::compressAssociative($data, $selectorKeys)`
`dropWhile`	Drop elements while predicate is true	`Single::dropWhile($data, $predicate)`
`filter`	Filter for elements where predicate is true	`Single::filterTrue($data, $predicate)`
`filterTrue`	Filter for truthy elements	`Single::filterTrue($data)`
`filterFalse`	Filter for falsy elements	`Single::filterFalse($data)`
`filterKeys`	Filter for keys where predicate is true	`Single::filterKeys($data, $predicate)`
`flatMap`	Map function onto items and flatten result	`Single::flaMap($data, $mapper)`
`flatten`	Flatten multidimensional iterable	`Single::flatten($data, [$dimensions])`
`groupBy`	Group data by a common element	`Single::groupBy($data, $groupKeyFunction, [$itemKeyFunc])`
`limit`	Iterate up to a limit	`Single::limit($data, $limit)`
`map`	Map function onto each item	`Single::map($data, $function)`
`pairwise`	Iterate successive overlapping pairs	`Single::pairwise($data)`
`reindex`	Reindex keys of key-value iterable	`Single::reindex($data, $reindexer)`
`repeat`	Repeat an item a number of times	`Single::repeat($item, $repetitions)`
`reverse`	Iterate elements in reverse order	`Single::reverse($data)`
`skip`	Iterate after skipping elements	`Single::skip($data, $count, [$offset])`
`slice`	Extract a slice of the iterable	`Single::slice($data, [$start], [$count], [$step])`
`string`	Iterate the characters of a string	`Single::string($string)`
`takeWhile`	Iterate elements while predicate is true	`Single::takeWhile($data, $predicate)`

Infinite Iteration

Iterator	Description	Code Snippet
`count`	Count sequentially forever	`Infinite::count($start, $step)`
`cycle`	Cycle through a collection	`Infinite::cycle($collection)`
`repeat`	Repeat an item forever	`Infinite::repeat($item)`

Random Iteration

Iterator	Description	Code Snippet
`choice`	Random selections from list	`Random::choice($list, $repetitions)`
`coinFlip`	Random coin flips (0 or 1)	`Random::coinFlip($repetitions)`
`number`	Random numbers	`Random::number($min, $max, $repetitions)`
`percentage`	Random percentage between 0 and 1	`Random::percentage($repetitions)`
`rockPaperScissors`	Random rock-paper-scissors hands	`Random::rockPaperScissors($repetitions)`

Math Iteration

Iterator	Description	Code Snippet
`frequencies`	Frequency distribution of data	`Math::frequencies($data, [$strict])`
`relativeFrequencies`	Relative frequency distribution of data	`Math::relativeFrequencies($data, [$strict])`
`runningAverage`	Running average accumulation	`Math::runningAverage($numbers, $initialValue)`
`runningDifference`	Running difference accumulation	`Math::runningDifference($numbers, $initialValue)`
`runningMax`	Running maximum accumulation	`Math::runningMax($numbers, $initialValue)`
`runningMin`	Running minimum accumulation	`Math::runningMin($numbers, $initialValue)`
`runningProduct`	Running product accumulation	`Math::runningProduct($numbers, $initialValue)`
`runningTotal`	Running total accumulation	`Math::runningTotal($numbers, $initialValue)`

Set and multiset Iteration

Iterator	Description	Code Snippet
`distinct`	Iterate only distinct items	`Set::distinct($data)`
`distinctBy`	Iterate only distinct items using custom comparator	`Set::distinct($data, $compareBy)`
`intersection`	Intersection of iterables	`Set::intersection(...$iterables)`
`intersectionCoercive`	Intersection with type coercion	`Set::intersectionCoercive(...$iterables)`
`partialIntersection`	Partial intersection of iterables	`Set::partialIntersection($minCount, ...$iterables)`
`partialIntersectionCoercive`	Partial intersection with type coercion	`Set::partialIntersectionCoercive($minCount, ...$iterables)`
`symmetricDifference`	Symmetric difference of iterables	`Set::symmetricDifference(...$iterables)`
`symmetricDifferenceCoercive`	Symmetric difference with type coercion	`Set::symmetricDifferenceCoercive(...$iterables)`
`union`	Union of iterables	`Set::union(...$iterables)`
`unionCoercive`	Union with type coercion	`Set::unionCoercive(...$iterables)`

Sort Iteration

Iterator	Description	Code Snippet
`asort`	Iterate a sorted collection maintaining keys	`Sort::asort($data, [$comparator])`
`sort`	Iterate a sorted collection	`Sort::sort($data, [$comparator])`

File Iteration

Iterator	Description	Code Snippet
`readCsv`	Intersection a CSV file line by line	`File::readCsv($fileHandle)`
`readLines`	Iterate a file line by line	`File::readLines($fileHandle)`

Transform Iteration

Iterator	Description	Code Snippet
`tee`	Iterate duplicate iterators	`Transform::tee($data, $count)`
`toArray`	Transform iterable to an array	`Transform::toArray($data)`
`toAssociativeArray`	Transform iterable to an associative array	`Transform::toAssociativeArray($data, [$keyFunc], [$valueFunc])`
`toIterator`	Transform iterable to an iterator	`Transform::toIterator($data)`

Summary

Summary	Description	Code Snippet
`allMatch`	True if all items are true according to predicate	`Summary::allMatch($data, $predicate)`
`allUnique`	True if all items are unique	`Summary::allUnique($data, [$strict])`
`anyMatch`	True if any item is true according to predicate	`Summary::anyMatch($data, $predicate)`
`arePermutations`	True if iterables are permutations of each other	`Summary::arePermutations(...$iterables)`
`arePermutationsCoercive`	True if iterables are permutations of each other with type coercion	`Summary::arePermutationsCoercive(...$iterables)`
`exactlyN`	True if exactly n items are true according to predicate	`Summary::exactlyN($data, $n, $predicate)`
`isEmpty`	True if iterable has no items	`Summary::isEmpty($data)`
`isPartitioned`	True if partitioned with items true according to predicate before others	`Summary::isPartitioned($data, $predicate)`
`isSorted`	True if iterable sorted	`Summary::isSorted($data)`
`isReversed`	True if iterable reverse sorted	`Summary::isReversed($data)`
`noneMatch`	True if none of items true according to predicate	`Summary::noneMatch($data, $predicate)`
`same`	True if iterables are the same	`Summary::same(...$iterables)`
`sameCount`	True if iterables have the same lengths	`Summary::sameCount(...$iterables)`

Reduce

Reducer	Description	Code Snippet
`toAverage`	Mean average of elements	`Reduce::toAverage($numbers)`
`toCount`	Reduce to length of iterable	`Reduce::toCount($data)`
`toFirst`	Reduce to its first value	`Reduce::toFirst($data)`
`toFirstAndLast`	Reduce to its first and last values	`Reduce::toFirstAndLast($data)`
`toLast`	Reduce to its last value	`Reduce::toLast()`
`toMax`	Reduce to its largest element	`Reduce::toMax($numbers, [$compareBy])`
`toMin`	Reduce to its smallest element	`Reduce::toMin($numbers, [$compareBy])`
`toMinMax`	Reduce to array of upper and lower bounds	`Reduce::toMinMax($numbers, [$compareBy])`
`toNth`	Reduce to value at nth position	`Reduce::toNth($data, $position)`
`toProduct`	Reduce to the product of its elements	`Reduce::toProduct($numbers)`
`toRandomValue`	Reduce to random value from iterable	`Reduce::toRandomValue($data)`
`toRange`	Reduce to difference of max and min values	`Reduce::toRange($numbers)`
`toString`	Reduce to joined string	`Reduce::toString($data, [$separator], [$prefix], [$suffix])`
`toSum`	Reduce to the sum of its elements	`Reduce::toSum($numbers)`
`toValue`	Reduce to value using callable reducer	`Reduce::toValue($data, $reducer, $initialValue)`

Stream Iteration Tools

Stream Sources

Source	Description	Code Snippet
`of`	Create a stream from an iterable	`Stream::of($iterable)`
`ofCoinFlips`	Create a stream of random coin flips	`Stream::ofCoinFlips($repetitions)`
`ofCsvFile`	Create a stream from a CSV file	`Stream::ofCsvFile($fileHandle)`
`ofEmpty`	Create an empty stream	`Stream::ofEmpty()`
`ofFileLines`	Create a stream from lines of a file	`Stream::ofFileLines($fileHandle)`
`ofRandomChoice`	Create a stream of random selections	`Stream::ofRandomChoice($items, $repetitions)`
`ofRandomNumbers`	Create a stream of random numbers (integers)	`Stream::ofRandomNumbers($min, $max, $repetitions)`
`ofRandomPercentage`	Create a stream of random percentages between 0 and 1	`Stream::ofRandomPercentage($repetitions)`
`ofRange`	Create a stream of a range of numbers	`Stream::ofRange($start, $end, $step)`
`ofRockPaperScissors`	Create a stream of rock-paper-scissors hands	`Stream::ofRockPaperScissors($repetitions)`

Stream Operations

Operation	Description	Code Snippet
`asort`	Sorts the iterable source maintaining keys	`$stream->asort([$comparator])`
`chainWith`	Chain iterable source withs given iterables together into a single iteration	`$stream->chainWith(...$iterables)`
`compress`	Compress source by filtering out data not selected	`$stream->compress($selectors)`
`compressAssociative`	Compress source by filtering out keys not selected	`$stream->compressAssociative($selectorKeys)`
`chunkwise`	Iterate by chunks	`$stream->chunkwise($chunkSize)`
`chunkwiseOverlap`	Iterate by overlapped chunks	`$stream->chunkwiseOverlap($chunkSize, $overlap)`
`distinct`	Filter out elements: iterate only unique items	`$stream->distinct([$strict])`
`distinctBy`	Filter out elements: iterate only unique items using custom comparator	`$stream->distinct($compareBy)`
`dropWhile`	Drop elements from the iterable source while the predicate function is true	`$stream->dropWhile($predicate)`
`filter`	Filter for only elements where the predicate function is true	`$stream->filterTrue($predicate)`
`filterTrue`	Filter for only truthy elements	`$stream->filterTrue()`
`filterFalse`	Filter for only falsy elements	`$stream->filterFalse()`
`filterKeys`	Filter for keys where predicate function is true	`$stream->filterKeys($predicate)`
`flatMap`	Map function onto elements and flatten result	`$stream->flatMap($function)`
`flatten`	Flatten multidimensional stream	`$stream->flatten($dimensions)`
`frequencies`	Frequency distribution	`$stream->frequencies([$strict])`
`groupBy`	Group iterable source by a common data element	`$stream->groupBy($groupKeyFunction, [$itemKeyFunc])`
`infiniteCycle`	Cycle through the elements of iterable source sequentially forever	`$stream->infiniteCycle()`
`intersectionWith`	Intersect iterable source and given iterables	`$stream->intersectionWith(...$iterables)`
`intersection CoerciveWith`	Intersect iterable source and given iterables with type coercion	`$stream->intersectionCoerciveWith(...$iterables)`
`limit`	Limit the stream's iteration	`$stream->limit($limit)`
`map`	Map function onto elements	`$stream->map($function)`
`pairwise`	Return pairs of elements from iterable source	`$stream->pairwise()`
`partialIntersectionWith`	Partially intersect iterable source and given iterables	`$stream->partialIntersectionWith( $minIntersectionCount, ...$iterables)`
`partialIntersection CoerciveWith`	Partially intersect iterable source and given iterables with type coercion	`$stream->partialIntersectionCoerciveWith( $minIntersectionCount, ...$iterables)`
`reindex`	Reindex keys of key-value stream	`$stream->reindex($reindexer)`
`relativeFrequencies`	Relative frequency distribution	`$stream->relativeFrequencies([$strict])`
`reverse`	Reverse elements of the stream	`$stream->reverse()`
`runningAverage`	Accumulate the running average (mean) over iterable source	`$stream->runningAverage($initialValue)`
`runningDifference`	Accumulate the running difference over iterable source	`$stream->runningDifference($initialValue)`
`runningMax`	Accumulate the running max over iterable source	`$stream->runningMax($initialValue)`
`runningMin`	Accumulate the running min over iterable source	`$stream->runningMin($initialValue)`
`runningProduct`	Accumulate the running product over iterable source	`$stream->runningProduct($initialValue)`
`runningTotal`	Accumulate the running total over iterable source	`$stream->runningTotal($initialValue)`
`skip`	Skip some elements of the stream	`$stream->skip($count, [$offset])`
`slice`	Extract a slice of the stream	`$stream->slice([$start], [$count], [$step])`
`sort`	Sorts the stream	`$stream->sort([$comparator])`
`symmetricDifferenceWith`	Symmetric difference of iterable source and given iterables	`$this->symmetricDifferenceWith(...$iterables)`
`symmetricDifference CoerciveWith`	Symmetric difference of iterable source and given iterables with type coercion	`$this->symmetricDifferenceCoerciveWith( ...$iterables)`
`takeWhile`	Return elements from the iterable source as long as the predicate is true	`$stream->takeWhile($predicate)`
`unionWith`	Union of stream with iterables	`$stream->unionWith(...$iterables)`
`unionCoerciveWith`	Union of stream with iterables with type coercion	`$stream->unionCoerciveWith(...$iterables)`
`zipWith`	Iterate iterable source with another iterable collection simultaneously	`$stream->zipWith(...$iterables)`
`zipEqualWith`	Iterate iterable source with another iterable collection of equal lengths simultaneously	`$stream->zipEqualWith(...$iterables)`
`zipFilledWith`	Iterate iterable source with another iterable collection using default filler	`$stream->zipFilledWith($default, ...$iterables)`
`zipLongestWith`	Iterate iterable source with another iterable collection simultaneously	`$stream->zipLongestWith(...$iterables)`

Stream Terminal Operations

Summary Terminal Operations

Terminal Operation	Description	Code Snippet
`allMatch`	Returns true if all items in stream match predicate	`$stream->allMatch($predicate)`
`allUnique`	Returns true if all items in stream are unique	`$stream->allUnique([$strict]])`
`anyMatch`	Returns true if any item in stream matches predicate	`$stream->anyMatch($predicate)`
`arePermutationsWith`	Returns true if all iterables permutations of stream	`$stream->arePermutationsWith(...$iterables)`
`arePermutationsCoerciveWith`	Returns true if all iterables permutations of stream with type coercion	`$stream->arePermutationsCoerciveWith(...$iterables)`
`exactlyN`	Returns true if exactly n items are true according to predicate	`$stream->exactlyN($n, $predicate)`
`isEmpty`	Returns true if stream has no items	`$stream::isEmpty()`
`isPartitioned`	Returns true if partitioned with items true according to predicate before others	`$stream::isPartitioned($predicate)`
`isSorted`	Returns true if stream is sorted in ascending order	`$stream->isSorted()`
`isReversed`	Returns true if stream is sorted in reverse descending order	`$stream->isReversed()`
`noneMatch`	Returns true if none of the items in stream match predicate	`$stream->noneMatch($predicate)`
`sameWith`	Returns true if stream and all given collections are the same	`$stream->sameWith(...$iterables)`
`sameCountWith`	Returns true if stream and all given collections have the same lengths	`$stream->sameCountWith(...$iterables)`

Reduction Terminal Operations

Terminal Operation	Description	Code Snippet
`toAverage`	Reduces stream to the mean average of its items	`$stream->toAverage()`
`toCount`	Reduces stream to its length	`$stream->toCount()`
`toFirst`	Reduces stream to its first value	`$stream->toFirst()`
`toFirstAndLast`	Reduces stream to its first and last values	`$stream->toFirstAndLast()`
`toLast`	Reduces stream to its last value	`$stream->toLast()`
`toMax`	Reduces stream to its max value	`$stream->toMax([$compareBy])`
`toMin`	Reduces stream to its min value	`$stream->toMin([$compareBy])`
`toMinMax`	Reduces stream to array of upper and lower bounds	`$stream->toMinMax([$compareBy])`
`toNth`	Reduces stream to value at nth position	`$stream->toNth($position)`
`toProduct`	Reduces stream to the product of its items	`$stream->toProduct()`
`toString`	Reduces stream to joined string	`$stream->toString([$separator], [$prefix], [$suffix])`
`toSum`	Reduces stream to the sum of its items	`$stream->toSum()`
`toRandomValue`	Reduces stream to random value within it	`$stream->toRandomValue()`
`toRange`	Reduces stream to difference of max and min values	`$stream->toRange()`
`toValue`	Reduces stream like array_reduce() function	`$stream->toValue($reducer, $initialValue)`

Transformation Terminal Operations

Terminal Operation	Description	Code Snippet
`toArray`	Returns array of stream elements	`$stream->toArray()`
`toAssociativeArray`	Returns key-value map of stream elements	`$stream->toAssociativeArray($keyFunc, $valueFunc)`
`tee`	Returns array of multiple identical Streams	`$stream->tee($count)`

Side Effect Terminal Operations

Terminal Operation	Description	Code Snippet
`callForEach`	Perform action via function on each item	`$stream->callForEach($function)`
`print`	`print` each item in the stream	`$stream->print([$separator], [$prefix], [$suffix])`
`printLn`	`print` each item on a new line	`$stream->printLn()`
`toCsvFile`	Write the contents of the stream to a CSV file	`$stream->toCsvFile($fileHandle, [$headers])`
`toFile`	Write the contents of the stream to a file	`$stream->toFile($fileHandle)`

Stream Debug Operations

Debug Operation	Description	Code Snippet
`peek`	Peek at each element between stream operations	`$stream->peek($peekFunc)`
`peekStream`	Peek at the entire stream between operations	`$stream->peekStream($peekFunc)`
`peekPrint`	Peek at each element by printing between operations	`$stream->peekPrint()`
`peekPrintR`	Peek at each element by doing print-r between operations	`$stream->peekPrintR()`
`printR`	`print_r` each item	`$stream->printR()`
`varDump`	`var_dump` each item	`$stream->varDump()`

Setup

Add the library to your composer.json file in your project:

{
  "require": {
      "markrogoyski/itertools-php": "1.*"
  }
}

Use composer to install the library:

$ php composer.phar install

Composer will install IterTools inside your vendor folder. Then you can add the following to your .php files to use the library with Autoloading.

require_once __DIR__ . '/vendor/autoload.php';

Alternatively, use composer on the command line to require and install IterTools:

$ php composer.phar require markrogoyski/itertools-php:1.*

Minimum Requirements

PHP 7.4

Usage

All functions work on iterable collections:

array (type)
Generator (type)
Iterator (interface)
Traversable (interface)

Multi Iteration

Chain

Chain multiple iterables together into a single continuous sequence.

Multi::chain(iterable ...$iterables)

use IterTools\Multi;

$prequels  = ['Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith'];
$originals = ['A New Hope', 'Empire Strikes Back', 'Return of the Jedi'];

foreach (Multi::chain($prequels, $originals) as $movie) {
    print($movie);
}
// 'Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith', 'A New Hope', 'Empire Strikes Back', 'Return of the Jedi'

Zip

Iterate multiple iterable collections simultaneously.

Multi::zip(iterable ...$iterables)

use IterTools\Multi;

$languages = ['PHP', 'Python', 'Java', 'Go'];
$mascots   = ['elephant', 'snake', 'bean', 'gopher'];

foreach (Multi::zip($languages, $mascots) as [$language, $mascot]) {
    print("The {$language} language mascot is an {$mascot}.");
}
// The PHP language mascot is an elephant.
// ...

Zip works with multiple iterable inputs--not limited to just two.

$names          = ['Ryu', 'Ken', 'Chun Li', 'Guile'];
$countries      = ['Japan', 'USA', 'China', 'USA'];
$signatureMoves = ['hadouken', 'shoryuken', 'spinning bird kick', 'sonic boom'];

foreach (Multi::zip($names, $countries, $signatureMoves) as [$name, $country, $signatureMove]) {
    $streetFighter = new StreetFighter($name, $country, $signatureMove);
}

Note: For uneven lengths, iteration stops when the shortest iterable is exhausted.

ZipEqual

Iterate multiple iterable collections with equal lengths simultaneously.

Throws \LengthException if lengths are not equal, meaning that at least one iterator ends before the others.

Multi::zipEqual(iterable ...$iterables)

use IterTools\Multi;

$letters = ['A', 'B', 'C'];
$numbers = [1, 2, 3];

foreach (Multi::zipEqual($letters, $numbers) as [$letter, $number]) {
    // ['A', 1], ['B', 2], ['C', 3]
}

ZipFilled

Iterate multiple iterable collections simultaneously, using a default filler value if lengths are not equal.

Multi::zipFilled(mixed $filler, iterable ...$iterables)

use IterTools\Multi;

$default = '?';
$letters = ['A', 'B'];
$numbers = [1, 2, 3];

foreach (Multi::zipFilled($default, $letters, $numbers) as [$letter, $number]) {
    // ['A', 1], ['B', 2], ['?', 3]
}

ZipLongest

Iterate multiple iterable collections simultaneously.

Multi::zipLongest(iterable ...$iterables)

For uneven lengths, the exhausted iterables will produce null for the remaining iterations.

use IterTools\Multi;

$letters = ['A', 'B', 'C'];
$numbers = [1, 2];

foreach (Multi::zipLongest($letters, $numbers) as [$letter, $number]) {
    // ['A', 1], ['B', 2], ['C', null]
}

Single Iteration

Chunkwise

Return elements in chunks of a certain size.

Single::chunkwise(iterable $data, int $chunkSize)

Chunk size must be at least 1.

use IterTools\Single;

$movies = [
    'Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith',
    'A New Hope', 'Empire Strikes Back', 'Return of the Jedi',
    'The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker'
];

foreach (Single::chunkwise($movies, 3) as $trilogy) {
    $trilogies[] = $trilogy;
}
// [
//     ['Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith'],
//     ['A New Hope', 'Empire Strikes Back', 'Return of the Jedi'],
//     ['The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker]'
// ]

Chunkwise Overlap

Return overlapped chunks of elements.

Single::chunkwiseOverlap(iterable $data, int $chunkSize, int $overlapSize, bool $includeIncompleteTail = true)

Chunk size must be at least 1.
Overlap size must be less than chunk size.

use IterTools\Single;

$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

foreach (Single::chunkwiseOverlap($numbers, 3, 1) as $chunk) {
    // [1, 2, 3], [3, 4, 5], [5, 6, 7], [7, 8, 9], [9, 10]
}

Compress

Compress an iterable by filtering out data that is not selected.

Single::compress(string $data, $selectors)

use IterTools\Single;

$movies = [
    'Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith',
    'A New Hope', 'Empire Strikes Back', 'Return of the Jedi',
    'The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker'
];
$goodMovies = [0, 0, 0, 1, 1, 1, 1, 0, 0];

foreach (Single::compress($movies, $goodMovies) as $goodMovie) {
    print($goodMovie);
}
// 'A New Hope', 'Empire Strikes Back', 'Return of the Jedi', 'The Force Awakens'

Compress Associative

Compress an iterable by filtering out keys that are not selected.

Single::compressAssociative(string $data, array $selectorKeys)

Standard PHP array/iterator keys only (string, integer).

use IterTools\Single;

$starWarsEpisodes = [
    'I'    => 'The Phantom Menace',
    'II'   => 'Attack of the Clones',
    'III'  => 'Revenge of the Sith',
    'IV'   => 'A New Hope',
    'V'    => 'The Empire Strikes Back',
    'VI'   => 'Return of the Jedi',
    'VII'  => 'The Force Awakens',
    'VIII' => 'The Last Jedi',
    'IX'   => 'The Rise of Skywalker',
];
$originalTrilogyNumbers = ['IV', 'V', 'VI'];

foreach (Single::compressAssociative($starWarsEpisodes, $originalTrilogyNumbers) as $episode => $title) {
    print("$episode: $title" . \PHP_EOL);
}
// IV: A New Hope
// V: The Empire Strikes Back
// VI: Return of the Jedi

Drop While

Drop elements from the iterable while the predicate function is true.

Once the predicate function returns false once, all remaining elements are returned.

Single::dropWhile(iterable $data, callable $predicate)

use IterTools\Single;

$scores    = [50, 60, 70, 85, 65, 90];
$predicate = fn ($x) => $x < 70;

foreach (Single::dropWhile($scores, $predicate) as $score) {
    print($score);
}
// 70, 85, 65, 90

Filter

Filter out elements from the iterable only returning elements where the predicate function is true.

Single::filter(iterable $data, callable $predicate)

use IterTools\Single;

$starWarsEpisodes   = [1, 2, 3, 4, 5, 6, 7, 8, 9];
$goodMoviePredicate = fn ($episode) => $episode > 3 && $episode < 8;

foreach (Single::filter($starWarsEpisodes, $goodMoviePredicate) as $goodMovie) {
    print($goodMovie);
}
// 4, 5, 6, 7

Filter True

Filter out elements from the iterable only returning elements that are truthy.

Single::filterTrue(iterable $data)

use IterTools\Single;

$reportCardGrades = [100, 0, 95, 85, 0, 94, 0];

foreach (Single::filterTrue($reportCardGrades) as $goodGrade) {
    print($goodGrade);
}
// 100, 95, 85, 94

Filter False

Filter out elements from the iterable only returning elements where the predicate function is false.

If no predicate is provided, the boolean value of the data is used.

Single::filterFalse(iterable $data, callable $predicate)

use IterTools\Single;

$alerts = [0, 1, 1, 0, 1, 0, 0, 1, 1];

foreach (Single::filterFalse($alerts) as $noAlert) {
    print($noAlert);
}
// 0, 0, 0, 0

Filter Keys

Filter out elements from the iterable only returning elements for which keys the predicate function is true.

Single::filterKeys(iterable $data, callable $predicate)

use IterTools\Single;

$olympics = [
    2000 => 'Sydney',
    2002 => 'Salt Lake City',
    2004 => 'Athens',
    2006 => 'Turin',
    2008 => 'Beijing',
    2010 => 'Vancouver',
    2012 => 'London',
    2014 => 'Sochi',
    2016 => 'Rio de Janeiro',
    2018 => 'Pyeongchang',
    2020 => 'Tokyo',
    2022 => 'Beijing',
];

$summerFilter = fn ($year) => $year % 4 === 0;

foreach (Single::filterKeys($olympics, $summerFilter) as $year => $hostCity) {
    print("$year: $hostCity" . \PHP_EOL);
}
// 2000: Sydney
// 2004: Athens
// 2008: Beijing
// 2012: London
// 2016: Rio de Janeiro
// 2020: Tokyo

Flat Map

Map a function only the elements of the iterable and then flatten the results.

Single::flatMap(iterable $data, callable $mapper)

use IterTools\Single;

$data   = [1, 2, 3, 4, 5];
$mapper = fn ($item) => [$item, -$item];

foreach (Single::flatMap($data, $mapper) as $number) {
    print($number . ' ');
}
// 1 -1 2 -2 3 -3 4 -4 5 -5

Flatten

Flatten a multidimensional iterable.

Single::flatten(iterable $data, int $dimensions = 1)

use IterTools\Single;

$multidimensional = [1, [2, 3], [4, 5]];

$flattened = [];
foreach (Single::flatten($multidimensional) as $number) {
    $flattened[] = $number;
}
// [1, 2, 3, 4, 5]

Group By

Group data by a common data element.

Single::groupBy(iterable $data, callable $groupKeyFunction, callable $itemKeyFunction = null)

The $groupKeyFunction determines the key to group elements by.
The optional $itemKeyFunction allows custom indexes within each group member.

use IterTools\Single;

$cartoonCharacters = [
    ['Garfield', 'cat'],
    ['Tom', 'cat'],
    ['Felix', 'cat'],
    ['Heathcliff', 'cat'],
    ['Snoopy', 'dog'],
    ['Scooby-Doo', 'dog'],
    ['Odie', 'dog'],
    ['Donald', 'duck'],
    ['Daffy', 'duck'],
];

$charactersGroupedByAnimal = [];
foreach (Single::groupBy($cartoonCharacters, fn ($x) => $x[1]) as $animal => $characters) {
    $charactersGroupedByAnimal[$animal] = $characters;
}
/*
'cat' => [
    ['Garfield', 'cat'],
    ['Tom', 'cat'],
    ['Felix', 'cat'],
    ['Heathcliff', 'cat'],
],
'dog' => [
    ['Snoopy', 'dog'],
    ['Scooby-Doo', 'dog'],
    ['Odie', 'dog'],
],
'duck' => [
    ['Donald', 'duck'],
    ['Daffy', 'duck'],
*/

Limit

Iterate up to a limit.

Stops even if more data available if limit reached.

Single::limit(iterable $data, int $limit)

use IterTools\Single;

$matrixMovies = ['The Matrix', 'The Matrix Reloaded', 'The Matrix Revolutions', 'The Matrix Resurrections'];
$limit        = 1;

foreach (Single::limit($matrixMovies, $limit) as $goodMovie) {
    print($goodMovie);
}
// 'The Matrix' (and nothing else)

Map

Map a function onto each element.

Single::map(iterable $data, callable $function)

use IterTools\Single;

$grades               = [100, 99, 95, 98, 100];
$strictParentsOpinion = fn ($g) => $g === 100 ? 'A' : 'F';

foreach (Single::map($grades, $strictParentsOpinion) as $actualGrade) {
    print($actualGrade);
}
// A, F, F, F, A

Pairwise

Returns successive overlapping pairs.

Returns empty generator if given collection contains fewer than 2 elements.

Single::pairwise(iterable $data)

use IterTools\Single;

$friends = ['Ross', 'Rachel', 'Chandler', 'Monica', 'Joey', 'Phoebe'];

foreach (Single::pairwise($friends) as [$leftFriend, $rightFriend]) {
    print("{$leftFriend} and {$rightFriend}");
}
// Ross and Rachel, Rachel and Chandler, Chandler and Monica, ...

Repeat

Repeat an item.

Single::repeat(mixed $item, int $repetitions)

use IterTools\Single;

$data        = 'Beetlejuice';
$repetitions = 3;

foreach (Single::repeat($data, $repetitions) as $repeated) {
    print($repeated);
}
// 'Beetlejuice', 'Beetlejuice', 'Beetlejuice'

Reindex

Reindex keys of key-value iterable using indexer function.

Single::reindex(string $data, callable $indexer)

use IterTools\Single;

$data = [
    [
        'title'   => 'Star Wars: Episode IV – A New Hope',
        'episode' => 'IV',
        'year'    => 1977,
    ],
    [
        'title'   => 'Star Wars: Episode V – The Empire Strikes Back',
        'episode' => 'V',
        'year'    => 1980,
    ],
    [
        'title' => 'Star Wars: Episode VI – Return of the Jedi',
        'episode' => 'VI',
        'year' => 1983,
    ],
];
$reindexFunc = fn (array $swFilm) => $swFilm['episode'];

$reindexedData = [];
foreach (Single::reindex($data, $reindexFunc) as $key => $filmData) {
    $reindexedData[$key] = $filmData;
}
// [
//     'IV' => [
//         'title'   => 'Star Wars: Episode IV – A New Hope',
//         'episode' => 'IV',
//         'year'    => 1977,
//     ],
//     'V' => [
//         'title'   => 'Star Wars: Episode V – The Empire Strikes Back',
//         'episode' => 'V',
//         'year'    => 1980,
//     ],
//     'VI' => [
//         'title' => 'Star Wars: Episode VI – Return of the Jedi',
//         'episode' => 'VI',
//         'year' => 1983,
//     ],
// ]

Reverse

Reverse the elements of an iterable.

Single::reverse(iterable $data)

use IterTools\Single;

$words = ['Alice', 'answers', 'your', 'questions', 'Bob'];

foreach (Single::reverse($words) as $word) {
    print($word . ' ');
}
// Bob questions your answers Alice

Skip

Skip n elements in the iterable after optional offset offset.

Single::skip(iterable $data, int $count, int $offset = 0)

use IterTools\Single;

$movies = [
    'The Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith',
    'A New Hope', 'The Empire Strikes Back', 'Return of the Jedi',
    'The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker'
];

$prequelsRemoved = [];
foreach (Single::skip($movies, 3) as $nonPrequel) {
    $prequelsRemoved[] = $nonPrequel;
} // Episodes IV - IX

$onlyTheBest = [];
foreach (Single::skip($prequelsRemoved, 3, 3) as $nonSequel) {
    $onlyTheBest[] = $nonSequel;
}
// 'A New Hope', 'The Empire Strikes Back', 'Return of the Jedi'

Slice

Extract a slice of the iterable.

Single::slice(iterable $data, int $start = 0, int $count = null, int $step = 1)

use IterTools\Single;

$olympics = [1992, 1994, 1996, 1998, 2000, 2002, 2004, 2006, 2008, 2010, 2012, 2014, 2016, 2018, 2020, 2022];
$winterOlympics = [];

foreach (Single::slice($olympics, 1, 8, 2) as $winterYear) {
    $winterOlympics[] = $winterYear;
}
// [1994, 1998, 2002, 2006, 2010, 2014, 2018, 2022]

String

Iterate the individual characters of a string.

Single::string(string $string)

use IterTools\Single;

$string = 'MickeyMouse';

$listOfCharacters = [];
foreach (Single::string($string) as $character) {
    $listOfCharacters[] = $character;
}
// ['M', 'i', 'c', 'k', 'e', 'y', 'M', 'o', 'u', 's', 'e']

Take While

Return elements from the iterable as long as the predicate is true.

Stops iteration as soon as the predicate returns false, even if other elements later on would eventually return true (different from filterTrue).

Single::takeWhile(iterable $data, callable $predicate)

use IterTools\Single;

$prices = [0, 0, 5, 10, 0, 0, 9];
$isFree = fn ($price) => $price == 0;

foreach (Single::takeWhile($prices, $isFree) as $freePrice) {
    print($freePrice);
}
// 0, 0

Infinite Iteration

Count

Count sequentially forever.

Infinite::count(int $start = 1, int $step = 1)

use IterTools\Infinite;

$start = 1;
$step  = 1;

foreach (Infinite::count($start, $step) as $i) {
    print($i);
}
// 1, 2, 3, 4, 5 ...

Cycle

Cycle through the elements of a collection sequentially forever.

Infinite::cycle(iterable $iterable)

use IterTools\Infinite;

$hands = ['rock', 'paper', 'scissors'];

foreach (Infinite::cycle($hands) as $hand) {
    RockPaperScissors::playHand($hand);
}
// rock, paper, scissors, rock, paper, scissors, ...

Repeat (Infinite)

Repeat an item forever.

Infinite::repeat(mixed $item)

use IterTools\Infinite;

$dialogue = 'Are we there yet?';

foreach (Infinite::repeat($dialogue) as $repeated) {
    print($repeated);
}
// 'Are we there yet?', 'Are we there yet?', 'Are we there yet?', ...

Random Iteration

Choice

Generate random selections from an array of values.

Random::choice(array $items, int $repetitions)

use IterTools\Random;

$cards       = ['Ace', 'King', 'Queen', 'Jack', 'Joker'];
$repetitions = 10;

foreach (Random::choice($cards, $repetitions) as $card) {
    print($card);
}
// 'King', 'Jack', 'King', 'Ace', ... [random]

CoinFlip

Generate random coin flips (0 or 1).

Random::coinFlip(int $repetitions)

use IterTools\Random;

$repetitions = 10;

foreach (Random::coinFlip($repetitions) as $coinFlip) {
    print($coinFlip);
}
// 1, 0, 1, 1, 0, ... [random]

Number

Generate random numbers (integers).

Random::number(int $min, int $max, int $repetitions)

use IterTools\Random;

$min         = 1;
$max         = 4;
$repetitions = 10;

foreach (Random::number($min, $max, $repetitions) as $number) {
    print($number);
}
// 3, 2, 5, 5, 1, 2, ... [random]

Percentage

Generate a random percentage between 0 and 1.

Random::percentage(int $repetitions)

use IterTools\Random;

$repetitions = 10;

foreach (Random::percentage($repetitions) as $percentage) {
    print($percentage);
}
// 0.30205562629132, 0.59648594775233, ... [random]

RockPaperScissors

Generate random rock-paper-scissors hands.

Random::rockPaperScissors(int $repetitions)

use IterTools\Random;

$repetitions = 10;

foreach (Random::rockPaperScissors($repetitions) as $rpsHand) {
    print($rpsHand);
}
// 'paper', 'rock', 'rock', 'scissors', ... [random]

Math Iteration

Frequencies

Returns a frequency distribution of the data.

Math::frequencies(iterable $data, bool $strict = true): \Generator

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Math;

$grades = ['A', 'A', 'B', 'B', 'B', 'C'];

foreach (Math::frequencies($grades) as $grade => $frequency) {
    print("$grade: $frequency" . \PHP_EOL);
}
// A: 2, B: 3, C: 1

Relative Frequencies

Returns a relative frequency distribution of the data.

Math::relativeFrequencies(iterable $data, bool $strict = true): \Generator

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Math;

$grades = ['A', 'A', 'B', 'B', 'B', 'C'];

foreach (Math::relativeFrequencies($grades) as $grade => $frequency) {
    print("$grade: $frequency" . \PHP_EOL);
}
// A: 0.33, B: 0.5, C: 0.166

Running Average

Accumulate the running average over a list of numbers.

Math::runningAverage(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$grades = [100, 80, 80, 90, 85];

foreach (Math::runningAverage($grades) as $runningAverage) {
    print($runningAverage);
}
// 100, 90, 86.667, 87.5, 87

Running Difference

Accumulate the running difference over a list of numbers.

Math::runningDifference(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$credits = [1, 2, 3, 4, 5];

foreach (Math::runningDifference($credits) as $runningDifference) {
    print($runningDifference);
}
// -1, -3, -6, -10, -15

Provide an optional initial value to lead off the running difference.

use IterTools\Math;

$dartsScores   = [50, 50, 25, 50];
$startingScore = 501;

foreach (Math::runningDifference($dartsScores, $startingScore) as $runningScore) {
    print($runningScore);
}
// 501, 451, 401, 376, 326

Running Max

Accumulate the running maximum over a list of numbers.

Math::runningMax(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$numbers = [1, 2, 1, 3, 5];

foreach (Math::runningMax($numbers) as $runningMax) {
    print($runningMax);
}
// 1, 2, 2, 3, 5

Running Min

Accumulate the running minimum over a list of numbers.

Math::runningMin(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$numbers = [3, 4, 2, 5, 1];

foreach (Math::runningMin($numbers) as $runningMin) {
    print($runningMin);
}
// 3, 3, 2, 2, 1

Running Product

Accumulate the running product over a list of numbers.

Math::runningProduct(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$numbers = [1, 2, 3, 4, 5];

foreach (Math::runningProduct($numbers) as $runningProduct) {
    print($runningProduct);
}
// 1, 2, 6, 24, 120

Provide an optional initial value to lead off the running product.

use IterTools\Math;

$numbers      = [1, 2, 3, 4, 5];
$initialValue = 5;

foreach (Math::runningProduct($numbers, $initialValue) as $runningProduct) {
    print($runningProduct);
}
// 5, 5, 10, 30, 120, 600

Running Total

Accumulate the running total over a list of numbers.

Math::runningTotal(iterable $numbers, int|float $initialValue = null)

use IterTools\Math;

$prices = [1, 2, 3, 4, 5];

foreach (Math::runningTotal($prices) as $runningTotal) {
    print($runningTotal);
}
// 1, 3, 6, 10, 15

Provide an optional initial value to lead off the running total.

use IterTools\Math;

$prices       = [1, 2, 3, 4, 5];
$initialValue = 5;

foreach (Math::runningTotal($prices, $initialValue) as $runningTotal) {
    print($runningTotal);
}
// 5, 6, 8, 11, 15, 20

Set and Multiset

Distinct

Filter out elements from the iterable only returning distinct elements.

Set::distinct(iterable $data, bool $strict = true)

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Set;

$chessSet = ['rook', 'rook', 'knight', 'knight', 'bishop', 'bishop', 'king', 'queen', 'pawn', 'pawn', ... ];

foreach (Set::distinct($chessSet) as $chessPiece) {
    print($chessPiece);
}
// rook, knight, bishop, king, queen, pawn

$mixedTypes = [1, '1', 2, '2', 3];

foreach (Set::distinct($mixedTypes, false) as $datum) {
    print($datum);
}
// 1, 2, 3

Distinct By

Filter out elements from the iterable only returning distinct elements according to a custom comparator function.

Set::distinctBy(iterable $data, callable $compareBy)

use IterTools\Set;

$streetFighterConsoleReleases = [
    ['id' => '112233', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'Dreamcast'],
    ['id' => '223344', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS4'],
    ['id' => '334455', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS5'],
    ['id' => '445566', 'name' => 'Street Fighter VI', 'console' => 'PS4'],
    ['id' => '556677', 'name' => 'Street Fighter VI', 'console' => 'PS5'],
    ['id' => '667788', 'name' => 'Street Fighter VI', 'console' => 'PC'],
];
$compareBy = fn ($sfTitle) => $sfTitle['name'];

$uniqueTitles = [];
foreach (Set::distinctBy($streetFighterConsoleReleases, $compareBy) as $sfTitle) {
    $uniqueTitles[] = $sfTitle;
}

// Contains one SF3 3rd Strike entry and one SFVI entry.

Intersection

Iterates intersection of iterables.

Set::intersection(iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$chessPieces = ['rook', 'knight', 'bishop', 'queen', 'king', 'pawn'];
$shogiPieces = ['rook', 'knight', 'bishop' 'king', 'pawn', 'lance', 'gold general', 'silver general'];

foreach (Set::intersection($chessPieces, $shogiPieces) as $commonPiece) {
    print($commonPiece);
}
// rook, knight, bishop, king, pawn

Intersection Coercive

Iterates intersection of iterables using type coercion.

Set::intersectionCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$numbers  = [1, 2, 3, 4, 5];
$numerics = ['1', '2', 3];

foreach (Set::intersectionCoercive($numbers, $numerics) as $commonNumber) {
    print($commonNumber);
}
// 1, 2, 3

Partial Intersection

Iterates M-partial intersection of iterables.

Set::partialIntersection(int $minIntersectionCount, iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$staticallyTyped    = ['c++', 'java', 'c#', 'go', 'haskell'];
$dynamicallyTyped   = ['php', 'python', 'javascript', 'typescript'];
$supportsInterfaces = ['php', 'java', 'c#', 'typescript'];

foreach (Set::partialIntersection(2, $staticallyTyped, $dynamicallyTyped, $supportsInterfaces) as $language) {
    print($language);
}
// c++, java, c#, go, php

Partial Intersection Coercive

Iterates M-partial intersection of iterables using type coercion.

Set::partialIntersectionCoercive(int $minIntersectionCount, iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$set1 = [1, 2, 3],
$set2 = ['2', '3', 4, 5],
$set3 = [1, '2'],

foreach (Set::partialIntersectionCoercive(2, $set1, $set2, $set3) as $partiallyCommonNumber) {
    print($partiallyCommonNumber);
}
// 1, 2, 3

Symmetric difference

Iterates the symmetric difference of iterables.

Set::symmetricDifference(iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

foreach (Set::symmetricDifference($a, $b, $c) as $item) {
    print($item);
}
// 1, 4, 5, 6, 7, 8, 9

Symmetric difference Coercive

Iterates the symmetric difference of iterables with type coercion.

Set::symmetricDifferenceCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

foreach (Set::symmetricDifferenceCoercive($a, $b, $c) as $item) {
    print($item);
}
// 4, 5, 6, 7, 8, 9

Union

Iterates the union of iterables.

Set::union(iterable ...$iterables)

If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Set;

$a = [1, 2, 3];
$b = [3, 4];
$c = [1, 2, 3, 6, 7];

foreach (Set::union($a, $b, $c) as $item) {
    print($item);
}
//1, 2, 3, 4, 6, 7

Union Coercive

Iterates the union of iterables with type coercion.

Set::unionCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Set;

$a = ['1', 2, 3];
$b = [3, 4];
$c = [1, 2, 3, 6, 7];

foreach (Set::unionCoercive($a, $b, $c) as $item) {
    print($item);
}
//1, 2, 3, 4, 6, 7

Sort Iteration

ASort

Iterate the collection sorted while maintaining the associative key index relations.

Sort::sort(iterable $data, callable $comparator = null)

Uses default sorting if optional comparator function not provided.

use IterTools\Single;

$worldPopulations = [
    'China'     => 1_439_323_776,
    'India'     => 1_380_004_385,
    'Indonesia' => 273_523_615,
    'Pakistan'  => 220_892_340,
    'USA'       => 331_002_651,
];

foreach (Sort::sort($worldPopulations) as $country => $population) {
    print("$country: $population" . \PHP_EOL);
}
// Pakistan: 220,892,340
// Indonesia: 273,523,615
// USA: 331,002,651
// India: 1,380,004,385
// China: 1,439,323,776

Sort

Iterate the collection sorted.

Sort::sort(iterable $data, callable $comparator = null)

Uses default sorting if optional comparator function not provided.

use IterTools\Single;

$data = [3, 4, 5, 9, 8, 7, 1, 6, 2];

foreach (Sort::sort($data) as $datum) {
    print($datum);
}
// 1, 2, 3, 4, 5, 6, 7, 8, 9

File

Read CSV

Iterate the lines of a CSV file.

File::readCsv(resource $fileHandle, string $separator = ',', string $enclosure = '"', string $escape = '\\')

use IterTools\File;

$fileHandle = \fopen('path/to/file.csv', 'r');

foreach (File::readCsv($fileHandle) as $row) {
    print_r($row);
}
// Each column field is an element of the array

Read Lines

Iterate the lines of a file.

File::readLines(resource $fileHandle)

use IterTools\File;

$fileHandle = \fopen('path/to/file.txt', 'r');

foreach (File::readLines($fileHandle) as $line) {
    print($line);
}

Transform

Tee

Return several independent (duplicated) iterators from a single iterable.

Transform::tee(iterable $data, int $count): array

use IterTools\Transform;

$daysOfWeek = ['Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat', 'Sun'];
$count = 3;

[$week1, $week2, $week3] = Transform::tee($data, $count);
// Each $week contains iterator containing ['Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat', 'Sun']

To Array

Transforms any iterable to an array.

Transform::toArray(iterable $data): array

use IterTools\Transform;

$iterator = new \ArrayIterator([1, 2, 3, 4, 5]);

$array = Transform::toArray($iterator);

To Associative Array

Transforms any iterable to an associative array.

Transform::toAssociativeArray(iterable $data, callable $keyFunc = null, callable $valueFunc = null): array

use IterTools\Transform;

$messages = ['message 1', 'message 2', 'message 3'];

$keyFunc   = fn ($msg) => \md5($msg);
$valueFunc = fn ($msg) => strtoupper($msg);

$associativeArray = Transform::toAssociativeArray($messages, $keyFunc, $valueFunc);
// [
//     '1db65a6a0a818fd39655b95e33ada11d' => 'MESSAGE 1',
//     '83b2330607fe8f817ce6d24249dea373' => 'MESSAGE 2',
//     '037805d3ad7b10c5b8425427b516b5ce' => 'MESSAGE 3',
// ]

To Iterator

Transforms any iterable to an iterator.

Transform::toArray(iterable $data): array

use IterTools\Transform;

$array = [1, 2, 3, 4, 5];

$iterator = Transform::toIterator($array);

Summary

All Match

Returns true if all elements match the predicate function.

Summary::allMatch(iterable $data, callable $predicate): bool

use IterTools\Summary;

$finalFantasyNumbers = [4, 5, 6];
$isOnSuperNintendo   = fn ($ff) => $ff >= 4 && $ff <= 6;

$boolean = Summary::allMatch($finalFantasyNumbers, $isOnSuperNintendo);
// true

$isOnPlaystation = fn ($ff) => $ff >= 7 && $ff <= 9;

$boolean = Summary::allMatch($finalFantasyNumbers, $isOnPlaystation);
// false

All Unique

Returns true if all elements are unique.

Summary::allUnique(iterable $data, bool $strict = true): bool

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Summary;

$items = ['fingerprints', 'snowflakes', 'eyes', 'DNA']

$boolean = Summary::allUnique($items);
// true

Any Match

Returns true if any element matches the predicate function.

Summary::anyMatch(iterable $data, callable $predicate): bool

use IterTools\Summary;

$answers          = ['fish', 'towel', 42, "don't panic"];
$isUltimateAnswer = fn ($a) => a == 42;

$boolean = Summary::anyMatch($answers, $isUltimateAnswer);
// true

Are Permutations

Returns true if all iterables are permutations of each other.

Summary::arePermutations(iterable ...$iterables): bool

use IterTools\Summary;

$iter = ['i', 't', 'e', 'r'];
$rite = ['r', 'i', 't', 'e'];
$reit = ['r', 'e', 'i', 't'];
$tier = ['t', 'i', 'e', 'r'];
$tire = ['t', 'i', 'r', 'e'];
$trie = ['t', 'r', 'i', 'e'];

$boolean = Summary::arePermutations($iter, $rite, $reit, $tier, $tire, $trie);
// true

Are Permutations Coercive

Returns true if all iterables are permutations of each other with type coercion.

Summary::arePermutationsCoercive(iterable ...$iterables): bool

use IterTools\Summary;

$set1 = [1, 2.0, '3'];
$set2 = [2.0, '1', 3];
$set3 = [3, 2, 1];

$boolean = Summary::arePermutationsCoercive($set1, $set2, $set3);
// true

Exactly N

Returns true if exactly n items are true according to a predicate function.

Predicate is optional.
Default predicate is boolean value of each item.

Summary::exactlyN(iterable $data, int $n, callable $predicate): bool

use IterTools\Summary;

$twoTruthsAndALie = [true, true, false];
$n                = 2;

$boolean = Summary::exactlyN($twoTruthsAndALie, $n);
// true

$ages      = [18, 21, 24, 54];
$n         = 4;
$predicate = fn ($age) => $age >= 21;

$boolean = Summary::exactlyN($ages, $n, $predicate);
// false

Is Empty

Returns true if the iterable is empty having no items.

Summary::isEmpty(iterable $data): bool

use IterTools\Summary;

$data = []

$boolean = Summary::isEmpty($data);
// true

Is Partitioned

Returns true if all elements of given collection that satisfy the predicate appear before all elements that don't.

Returns true for empty collection or for collection with single item.
Default predicate if not provided is the boolean value of each data item.

Summary::isPartitioned(iterable $data, callable $predicate = null): bool

use IterTools\Summary;

$numbers          = [0, 2, 4, 1, 3, 5];
$evensBeforeOdds = fn ($item) => $item % 2 === 0;

$boolean = Summary::isPartitioned($numbers, $evensBeforeOdds);

Is Sorted

Returns true if elements are sorted, otherwise false.

Elements must be comparable.
Returns true if empty or has only one element.

Summary::isSorted(iterable $data): bool

use IterTools\Summary;

$numbers = [1, 2, 3, 4, 5];

$boolean = Summary::isSorted($numbers);
// true

$numbers = [3, 2, 3, 4, 5];

$boolean = Summary::isSorted($numbers);
// false

Is Reversed

Returns true if elements are reverse sorted, otherwise false.

Elements must be comparable.
Returns true if empty or has only one element.

Summary::isReversed(iterable $data): bool

use IterTools\Summary;

$numbers = [5, 4, 3, 2, 1];

$boolean = Summary::isReversed($numbers);
// true

$numbers = [1, 4, 3, 2, 1];

$boolean = Summary::isReversed($numbers);
// false

None Match

Returns true if no element matches the predicate function.

Summary::noneMatch(iterable $data, callable $predicate): bool

use IterTools\Summary;

$grades         = [45, 50, 61, 0];
$isPassingGrade = fn ($grade) => $grade >= 70;

$boolean = Summary::noneMatch($grades, $isPassingGrade);
// true

Same

Returns true if all given collections are the same.

For single iterable or empty iterables list returns true.

Summary::same(iterable ...$iterables): bool

use IterTools\Summary;

$cocaColaIngredients = ['carbonated water', 'sugar', 'caramel color', 'phosphoric acid'];
$pepsiIngredients    = ['carbonated water', 'sugar', 'caramel color', 'phosphoric acid'];

$boolean = Summary::same($cocaColaIngredients, $pepsiIngredients);
// true

$cocaColaIngredients = ['carbonated water', 'sugar', 'caramel color', 'phosphoric acid'];
$spriteIngredients   = ['carbonated water', 'sugar', 'citric acid', 'lemon lime flavorings'];

$boolean = Summary::same($cocaColaIngredients, $spriteIngredients);
// false

Same Count

Returns true if all given collections have the same lengths.

For single iterable or empty iterables list returns true.

Summary::sameCount(iterable ...$iterables): bool

use IterTools\Summary;

$prequels  = ['Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith'];
$originals = ['A New Hope', 'Empire Strikes Back', 'Return of the Jedi'];
$sequels   = ['The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker'];

$boolean = Summary::sameCount($prequels, $originals, $sequels);
// true

$batmanMovies = ['Batman Begins', 'The Dark Knight', 'The Dark Knight Rises'];
$matrixMovies = ['The Matrix', 'The Matrix Reloaded', 'The Matrix Revolutions', 'The Matrix Resurrections'];

$result = Summary::sameCount($batmanMovies, $matrixMovies);
// false

Reduce

To Average

Reduces to the mean average.

Returns null if collection is empty.

Reduce::toAverage(iterable $data): float

use IterTools\Reduce;

$grades = [100, 90, 95, 85, 94];

$finalGrade = Reduce::toAverage($numbers);
// 92.8

To Count

Reduces iterable to its length.

Reduce::toCount(iterable $data): int

use IterTools\Reduce;

$someIterable = ImportantThing::getCollectionAsIterable();

$length = Reduce::toCount($someIterable);
// 3

To First

Reduces iterable to its first element.

Reduce::toFirst(iterable $data): mixed

Throws \LengthException if collection is empty.

use IterTools\Reduce;

$medals = ['gold', 'silver', 'bronze'];

$first = Reduce::toFirst($medals);
// gold

To First And Last

Reduces iterable to its first and last elements.

Reduce::toFirstAndLast(iterable $data): array{mixed, mixed}

Throws \LengthException if collection is empty.

use IterTools\Reduce;

$weekdays = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'];

$firstAndLast = Reduce::toFirstAndLast($weekdays);
// [Monday, Friday]

To Last

Reduces iterable to its last element.

Reduce::toLast(iterable $data): mixed

Throws \LengthException if collection is empty.

use IterTools\Reduce;

$gnomesThreePhasePlan = ['Collect underpants', '?', 'Profit'];

$lastPhase = Reduce::toLast($gnomesThreePhasePlan);
// Profit

To Max

Reduces to the max value.

Reduce::toMax(iterable $data, callable $compareBy = null): mixed|null

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns null if collection is empty.

use IterTools\Reduce;

$numbers = [5, 3, 1, 2, 4];

$result = Reduce::toMax($numbers);
// 5

$movieRatings = [
    [
        'title' => 'Star Wars: Episode IV - A New Hope',
        'rating' => 4.6
    ],
    [
        'title' => 'Star Wars: Episode V - The Empire Strikes Back',
        'rating' => 4.8
    ],
    [
        'title' => 'Star Wars: Episode VI - Return of the Jedi',
        'rating' => 4.6
    ],
];
$compareBy = fn ($movie) => $movie['rating'];

$highestRatedMovie = Reduce::toMax($movieRatings, $compareBy);
// [
//     'title' => 'Star Wars: Episode V - The Empire Strikes Back',
//     'rating' => 4.8
// ];

To Min

Reduces to the min value.

Reduce::toMin(iterable $data, callable $compareBy = null): mixed|null

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns null if collection is empty.

use IterTools\Reduce;

$numbers = [5, 3, 1, 2, 4];

$result = Reduce::toMin($numbers);
// 1


$movieRatings = [
    [
        'title' => 'The Matrix',
        'rating' => 4.7
    ],
    [
        'title' => 'The Matrix Reloaded',
        'rating' => 4.3
    ],
    [
        'title' => 'The Matrix Revolutions',
        'rating' => 3.9
    ],
    [
        'title' => 'The Matrix Resurrections',
        'rating' => 2.5
    ],
];
$compareBy = fn ($movie) => $movie['rating'];

$lowestRatedMovie = Reduce::toMin($movieRatings, $compareBy);
// [
//     'title' => 'The Matrix Resurrections',
//     'rating' => 2.5
// ]

To Min Max

Reduces to array of its upper and lower bounds (max and min).

Reduce::toMinMax(iterable $numbers, callable $compareBy = null): array

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns [null, null] if given collection is empty.

use IterTools\Reduce;

$numbers = [1, 2, 7, -1, -2, -3];

[$min, $max] = Reduce::toMinMax($numbers);
// [-3, 7]

$reportCard = [
    [
        'subject' => 'history',
        'grade' => 90
    ],
    [
        'subject' => 'math',
        'grade' => 98
    ],
    [
        'subject' => 'science',
        'grade' => 92
    ],
    [
        'subject' => 'english',
        'grade' => 85
    ],
    [
        'subject' => 'programming',
        'grade' => 100
    ],
];
$compareBy = fn ($class) => $class['grade'];

$bestAndWorstSubject = Reduce::toMinMax($reportCard, $compareBy);
// [
//     [
//         'subject' => 'english',
//         'grade' => 85
//     ],
//     [
//         'subject' => 'programming',
//         'grade' => 100
//     ],
// ]

To Nth

Reduces to value at the nth position.

Reduce::toNth(iterable $data, int $position): mixed

use IterTools\Reduce;

$lotrMovies = ['The Fellowship of the Ring', 'The Two Towers', 'The Return of the King'];

$rotk = Reduce::toNth($lotrMovies, 2);
// 20

To Product

Reduces to the product of its elements.

Returns null if collection is empty.

Reduce::toProduct(iterable $data): number|null

use IterTools\Reduce;

$primeFactors = [5, 2, 2];

$number = Reduce::toProduct($primeFactors);
// 20

To Random Value

Reduces given collection to a random value within it.

Reduce::toRandomValue(iterable $data): mixed

use IterTools\Reduce;

$sfWakeupOptions = ['mid', 'low', 'overhead', 'throw', 'meaty'];

$wakeupOption = Reduce::toRandomValue($sfWakeupOptions);
// e.g., throw

To Range

Reduces given collection to its range (difference between max and min).

Reduce::toRange(iterable $numbers): int|float

Returns 0 if iterable source is empty.

use IterTools\Reduce;

$grades = [100, 90, 80, 85, 95];

$range = Reduce::toRange($numbers);
// 20

To String

Reduces to a string joining all elements.

Optional separator to insert between items.
Optional prefix to prepend to the string.
Optional suffix to append to the string.

Reduce::toString(iterable $data, string $separator = '', string $prefix = '', string $suffix = ''): string

use IterTools\Reduce;

$words = ['IterTools', 'PHP', 'v1.0'];

$string = Reduce::toString($words);
// IterToolsPHPv1.0
$string = Reduce::toString($words, '-');
// IterTools-PHP-v1.0
$string = Reduce::toString($words, '-', 'Library: ');
// Library: IterTools-PHP-v1.0
$string = Reduce::toString($words, '-', 'Library: ', '!');
// Library: IterTools-PHP-v1.0!

To Sum

Reduces to the sum of its elements.

Reduce::toSum(iterable $data): number

use IterTools\Reduce;

$parts = [10, 20, 30];

$sum = Reduce::toSum($parts);
// 60

To Value

Reduce elements to a single value using reducer function.

Reduce::toValue(iterable $data, callable $reducer, mixed $initialValue): mixed

use IterTools\Reduce;

$input = [1, 2, 3, 4, 5];
$sum   = fn ($carry, $item) => $carry + $item;

$result = Reduce::toValue($input, $sum, 0);
// 15

Stream

Streams provide a fluent interface to transform arrays and iterables through a pipeline of operations.

Streams are made up of:

One stream source factory method to create the stream.
Zero or more stream operators that transform the stream to a new stream.

Terminal operation of either:

Stream terminal operation to transform the stream to a value or data structure.

$result = Stream::of([1, 1, 2, 2, 3, 4, 5])
   ->distinct()                  // [1, 2, 3, 4, 5]
   ->map(fn ($x) => $x**2)       // [1, 4, 9, 16, 25]
   ->filter(fn ($x) => $x < 10)  // [1, 4, 9]
   ->toSum();                    // 14

The stream is iterated via a foreach loop.

$result = Stream::of([1, 1, 2, 2, 3, 4, 5])
   ->distinct()                  // [1, 2, 3, 4, 5]
   ->map(fn ($x) => $x**2)       // [1, 4, 9, 16, 25]
   ->filter(fn ($x) => $x < 10); // [1, 4, 9]

foreach ($result as $item) {
    // 1, 4, 9
}

Stream Sources

Of

Creates stream from an iterable.

Stream::of(iterable $iterable): Stream

use IterTools\Stream;

$iterable = [1, 2, 3];

$result = Stream::of($iterable)
    ->chainWith([4, 5, 6], [7, 8, 9])
    ->zipEqualWith([1, 2, 3, 4, 5, 6, 7, 8, 9])
    ->toValue(fn ($carry, $item) => $carry + array_sum($item));
// 90

Of Coin Flips

Creates stream of n random coin flips.

Stream::ofCoinFlips(int $repetitions): Stream

use IterTools\Stream;

$result = Stream::ofCoinFlips(10)
    ->filterTrue()
    ->toCount();
// 5 (random)

Of CSV File

Creates a stream of rows of a CSV file.

Stream::ofCsvFile(resource $fileHandle, string $separator = ',', string $enclosure = '"', string = $escape = '\\'): Stream

use IterTools\Stream;

$fileHandle = \fopen('path/to/file.csv', 'r');

$result = Stream::of($fileHandle)
    ->toArray();

Of Empty

Creates stream of nothing.

Stream::ofEmpty(): Stream

use IterTools\Stream;

$result = Stream::ofEmpty()
    ->chainWith([1, 2, 3])
    ->toArray();
// 1, 2, 3

Of File Lines

Creates a stream of lines of a file.

Stream::ofFileLines(resource $fileHandle): Stream

use IterTools\Stream;

$fileHandle = \fopen('path/to/file.txt', 'r');

$result = Stream::of($fileHandle)
    ->map('strtoupper');
    ->toArray();

Of Random Choice

Creates stream of random selections from an array of values.

Stream::ofRandomChoice(array $items, int $repetitions): Stream

use IterTools\Stream;

$languages = ['PHP', 'Go', 'Python'];

$languages = Stream::ofRandomChoice($languages, 5)
    ->toArray();
// 'Go', 'PHP', 'Python', 'PHP', 'PHP' (random)

Of Random Numbers

Creates stream of random numbers (integers).

Stream::ofRandomNumbers(int $min, int $max, int $repetitions): Stream

use IterTools\Stream;

$min  = 1;
$max  = 3;
$reps = 7;

$result = Stream::ofRandomNumbers($min, $max, $reps)
    ->toArray();
// 1, 2, 2, 1, 3, 2, 1 (random)

Of Random Percentage

Creates stream of random percentages between 0 and 1.

Stream::ofRandomPercentage(int $repetitions): Stream

use IterTools\Stream;

$stream = Stream::ofRandomPercentage(3)
    ->toArray();
// 0.8012566976245, 0.81237281724151, 0.61676896329459 [random]

Of Range

Creates stream of a range of numbers.

Stream::ofRange(int|float $start, int|float $end, int|float $step = 1): Stream

use IterTools\Stream;

$numbers = Stream::ofRange(0, 5)
    ->toArray();
// 0, 1, 2, 3, 4, 5

Of Rock Paper Scissors

Creates stream of rock-paper-scissors hands.

Stream::ofRockPaperScissors(int $repetitions): Stream

use IterTools\Stream;

$rps = Stream::ofRockPaperScissors(5)
    ->toArray();
// 'paper', 'rock', 'rock', 'scissors', 'paper' [random]

Stream Operations

ASort

Sorts the stream, maintaining keys.

$stream->asort(callable $comparator = null)

If comparator is not provided, the elements of the iterable source must be comparable.

use IterTools\Stream;

$worldPopulations = [
    'China'     => 1_439_323_776,
    'India'     => 1_380_004_385,
    'Indonesia' => 273_523_615,
    'USA'       => 331_002_651,
];

$result = Stream::of($worldPopulations)
    ->filter(fn ($pop) => $pop > 300_000_000)
    ->asort()
    ->toAssociativeArray();
// USA   => 331_002_651,
// India => 1_380_004_385,
// China => 1_439_323_776,

Chain With

Return a stream chaining additional sources together into a single consecutive stream.

$stream->chainWith(iterable ...$iterables): Stream

use IterTools\Stream;

$input = [1, 2, 3];

$result = Stream::of($input)
    ->chainWith([4, 5, 6])
    ->chainWith([7, 8, 9])
    ->toArray();
// 1, 2, 3, 4, 5, 6, 7, 8, 9

Compress

Compress to a new stream by filtering out data that is not selected.

$stream->compress(iterable $selectors): Stream

Selectors indicate which data. True value selects item. False value filters out data.

use IterTools\Stream;

$input = [1, 2, 3];

$result = Stream::of($input)
    ->compress([0, 1, 1])
    ->toArray();
// 2, 3

Compress Associative

Compress to a new stream by filtering out keys that are not selected.

$stream->compressAssociative(array $keys): Stream

Standard PHP array/iterator keys only (string, integer).

use IterTools\Stream;

$starWarsEpisodes = [
    'I'    => 'The Phantom Menace',
    'II'   => 'Attack of the Clones',
    'III'  => 'Revenge of the Sith',
    'IV'   => 'A New Hope',
    'V'    => 'The Empire Strikes Back',
    'VI'   => 'Return of the Jedi',
    'VII'  => 'The Force Awakens',
    'VIII' => 'The Last Jedi',
    'IX'   => 'The Rise of Skywalker',
];
$sequelTrilogyNumbers = ['VII', 'VIII', 'IX'];

$sequelTrilogy = Stream::of($starWarsEpisodes)
    ->compressAssociative($sequelTrilogyNumbers)
    ->toAssociativeArray();
// 'VII'  => 'The Force Awakens',
// 'VIII' => 'The Last Jedi',
// 'IX'   => 'The Rise of Skywalker',

Chunkwise

Return a stream consisting of chunks of elements from the stream.

$stream->chunkwise(int $chunkSize): Stream

Chunk size must be at least 1.

use IterTools\Stream;

$friends = ['Ross', 'Rachel', 'Chandler', 'Monica', 'Joey'];

$result = Stream::of($friends)
    ->chunkwise(2)
    ->toArray();
// ['Ross', 'Rachel'], ['Chandler', 'Monica'], ['Joey']

Chunkwise Overlap

Return a stream consisting of overlapping chunks of elements from the stream.

$stream->chunkwiseOverlap(int $chunkSize, int $overlapSize, bool $includeIncompleteTail = true): Stream

Chunk size must be at least 1.
Overlap size must be less than chunk size.

use IterTools\Stream;

$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9];

$result = Stream::of($friends)
    ->chunkwiseOverlap(3, 1)
    ->toArray()
// [1, 2, 3], [3, 4, 5], [5, 6, 7], [7, 8, 9]

Distinct

Return a stream filtering out elements from the stream only returning distinct elements.

$stream->distinct(bool $strict = true): Stream

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Stream;

$input = [1, 2, 1, 2, 3, 3, '1', '1', '2', '3'];
$stream = Stream::of($input)
    ->distinct()
    ->toArray();
// 1, 2, 3, '1', '2', '3'

$stream = Stream::of($input)
    ->distinct(false)
    ->toArray();
// 1, 2, 3

Distinct By

Return a stream filtering out elements from the stream only returning distinct elements according to a custom comparator function.

$stream->distinctBy(callable $compareBy): Stream

use IterTools\Stream;

$streetFighterConsoleReleases = [
    ['id' => '112233', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'Dreamcast'],
    ['id' => '223344', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS4'],
    ['id' => '334455', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS5'],
    ['id' => '445566', 'name' => 'Street Fighter VI', 'console' => 'PS4'],
    ['id' => '556677', 'name' => 'Street Fighter VI', 'console' => 'PS5'],
    ['id' => '667799', 'name' => 'Street Fighter VI', 'console' => 'PC'],
];
$stream = Stream::of($streetFighterConsoleReleases)
    ->distinctBy(fn ($sfTitle) => $sfTitle['name'])
    ->toArray();
// Contains one SF3 3rd Strike entry and one SFVI entry

Drop While

Drop elements from the stream while the predicate function is true.

$stream->dropWhile(callable $predicate): Stream

Once the predicate function returns false once, all remaining elements are returned.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5]

$result = Stream::of($input)
    ->dropWhile(fn ($value) => $value < 3)
    ->toArray();
// 3, 4, 5

Filter

Filter out elements from the stream only keeping elements where there predicate function is true.

$stream->filter(callable $predicate): Stream

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($input)
    ->filter(fn ($value) => $value > 0)
    ->toArray();
// 1, 2, 3

Filter True

Filter out elements from the stream only keeping elements that are truthy.

$stream->filterTrue(): Stream

use IterTools\Stream;

$input = [0, 1, 2, 3, 0, 4];

$result = Stream::of($input)
    ->filterTrue()
    ->toArray();
// 1, 2, 3, 4

Filter False

Filter out elements from the stream only keeping elements that are falsy.

$stream->filterFalse(): Stream

use IterTools\Stream;

$input = [0, 1, 2, 3, 0, 4];

$result = Stream::of($input)
    ->filterFalse()
    ->toArray();
// 0, 0

Filter Keys

Filter out elements from stream only keeping elements where the predicate function on the keys are true.

$stream->filterKeys(callable $filter): Stream

$olympics = [
    2000 => 'Sydney',
    2002 => 'Salt Lake City',
    2004 => 'Athens',
    2006 => 'Turin',
    2008 => 'Beijing',
    2010 => 'Vancouver',
    2012 => 'London',
    2014 => 'Sochi',
    2016 => 'Rio de Janeiro',
    2018 => 'Pyeongchang',
    2020 => 'Tokyo',
    2022 => 'Beijing',
];

$winterFilter = fn ($year) => $year % 4 === 2;

$result = Stream::of($olympics)
    ->filterKeys($winterFilter)
    ->toAssociativeArray();
}
// 2002 => Salt Lake City
// 2006 => Turin
// 2010 => Vancouver
// 2014 => Sochi
// 2018 => Pyeongchang
// 2022 => Beijing

Flat Map

Map a function onto the elements of the stream and flatten the results.

$stream->flatMap(callable $mapper): Stream

$data    = [1, 2, 3, 4, 5];
$mapper  fn ($item) => ($item % 2 === 0) ? [$item, $item] : $item;

$result = Stream::of($data)
    ->flatMap($mapper)
    ->toArray();
// [1, 2, 2, 3, 4, 4, 5]

Flatten

Flatten a multidimensional stream.

$stream->flatten(int $dimensions = 1): Stream

$data = [1, [2, 3], [4, 5]];

$result = Stream::of($data)
    ->flatten($mapper)
    ->toArray();
// [1, 2, 3, 4, 5]

Frequencies

Frequency distribution of the stream elements.

$stream->frequencies(bool $strict = true): Stream

use IterTools\Stream;

$grades = ['A', 'A', 'B', 'B', 'B', 'C'];

$result = Stream::of($grades)
    ->frequencies()
    ->toAssociativeArray();

// ['A' => 2, 'B' => 3, 'C' => 1]

Group By

Return a stream grouping by a common data element.

$stream->groupBy(callable $groupKeyFunction, callable $itemKeyFunction = null): Stream

The $groupKeyFunction determines the key to group elements by.
The optional $itemKeyFunction allows custom indexes within each group member.

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$groups = Stream::of($input)
    ->groupBy(fn ($item) => $item > 0 ? 'positive' : 'negative');

foreach ($groups as $group => $item) {
    // 'positive' => [1, 2, 3], 'negative' => [-1, -2, -3]
}

Infinite Cycle

Return a stream cycling through the elements of stream sequentially forever.

$stream->infiniteCycle(): Stream

use IterTools\Stream;

$input = [1, 2, 3];

$result = Stream::of($input)
    ->infiniteCycle()
    ->print();
// 1, 2, 3, 1, 2, 3, ...

Intersection With

Return a stream intersecting the stream with the input iterables.

$stream->intersectionWith(iterable ...$iterables): Stream

use IterTools\Stream;

$numbers    = [1, 2, 3, 4, 5, 6, 7, 8, 9];
$numerics   = ['1', '2', 3, 4, 5, 6, 7, '8', '9'];
$oddNumbers = [1, 3, 5, 7, 9, 11];

$stream = Stream::of($numbers)
    ->intersectionWith($numerics, $oddNumbers)
    ->toArray();
// 3, 5, 7

Intersection Coercive With

Return a stream intersecting the stream with the input iterables using type coercion.

$stream->intersectionCoerciveWith(iterable ...$iterables): Stream

use IterTools\Stream;

$languages          = ['php', 'python', 'c++', 'java', 'c#', 'javascript', 'typescript'];
$scriptLanguages    = ['php', 'python', 'javascript', 'typescript'];
$supportsInterfaces = ['php', 'java', 'c#', 'typescript'];

$stream = Stream::of($languages)
    ->intersectionCoerciveWith($scriptLanguages, $supportsInterfaces)
    ->toArray();
// 'php', 'typescript'

Limit

Return a stream up to a limit.

Stops even if more data available if limit reached.

$stream->limit(int $limit): Stream

Use IterTools\Single;

$matrixMovies = ['The Matrix', 'The Matrix Reloaded', 'The Matrix Revolutions', 'The Matrix Resurrections'];
$limit        = 1;

$goodMovies = Stream::of($matrixMovies)
    ->limit($limit)
    ->toArray();
// 'The Matrix' (and nothing else)

Map

Return a stream containing the result of mapping a function onto each element of the stream.

$stream->map(callable $function): Stream

use IterTools\Stream;

$grades = [100, 95, 98, 89, 100];

$result = Stream::of($grades)
    ->map(fn ($grade) => $grade === 100 ? 'A' : 'F')
    ->toArray();
// A, F, F, F, A

Pairwise

Return a stream consisting of pairs of elements from the stream.

$stream->pairwise(): Stream

Returns empty stream if given collection contains less than 2 elements.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$stream = Stream::of($input)
    ->pairwise()
    ->toArray();
// [1, 2], [2, 3], [3, 4], [4, 5]

Partial Intersection With

Return a stream partially intersecting the stream with the input iterables.

$stream->partialIntersectionWith(int $minIntersectionCount, iterable ...$iterables): Stream

use IterTools\Stream;

$numbers    = [1, 2, 3, 4, 5, 6, 7, 8, 9];
$numerics   = ['1', '2', 3, 4, 5, 6, 7, '8', '9'];
$oddNumbers = [1, 3, 5, 7, 9, 11];

$stream = Stream::of($numbers)
    ->partialIntersectionWith($numerics, $oddNumbers)
    ->toArray();
// 1, 3, 4, 5, 6, 7, 9

Partial Intersection Coercive With

Return a stream partially intersecting the stream with the input iterables using type coercion.

$stream->partialIntersectionCoerciveWith(int $minIntersectionCount, iterable ...$iterables): Stream

use IterTools\Stream;

$languages          = ['php', 'python', 'c++', 'java', 'c#', 'javascript', 'typescript'];
$scriptLanguages    = ['php', 'python', 'javascript', 'typescript'];
$supportsInterfaces = ['php', 'java', 'c#', 'typescript'];

$stream = Stream::of($languages)
    ->partialIntersectionCoerciveWith(2, $scriptLanguages, $supportsInterfaces)
    ->toArray();
// 'php', 'python', 'java', 'typescript', 'c#', 'javascript'

Reindex

Return a new stream of key-value elements reindexed by the key indexer function.

$stream->reindex(callable $indexer): Stream

use IterTools\Stream;

$data = [
    [
        'title'   => 'Star Wars: Episode IV – A New Hope',
        'episode' => 'IV',
        'year'    => 1977,
    ],
    [
        'title'   => 'Star Wars: Episode V – The Empire Strikes Back',
        'episode' => 'V',
        'year'    => 1980,
    ],
    [
        'title' => 'Star Wars: Episode VI – Return of the Jedi',
        'episode' => 'VI',
        'year' => 1983,
    ],
];
$reindexFunc = fn (array $swFilm) => $swFilm['episode'];

$reindexResult = Stream::of($data)
    ->reindex($reindexFunc)
    ->toAssociativeArray();
// [
//     'IV' => [
//         'title'   => 'Star Wars: Episode IV – A New Hope',
//         'episode' => 'IV',
//         'year'    => 1977,
//     ],
//     'V' => [
//         'title'   => 'Star Wars: Episode V – The Empire Strikes Back',
//         'episode' => 'V',
//         'year'    => 1980,
//     ],
//     'VI' => [
//         'title' => 'Star Wars: Episode VI – Return of the Jedi',
//         'episode' => 'VI',
//         'year' => 1983,
//     ],
// ]

Relative Frequencies

Relative frequency distribution of the stream elements.

$stream->relativeFrequencies(bool $strict = true): Stream

use IterTools\Stream;

$grades = ['A', 'A', 'B', 'B', 'B', 'C'];

$result = Stream::of($grades)
    ->relativeFrequencies()
    ->toAssociativeArray();

// A => 0.33, B => 0.5, C => 0.166

Reverse

Reverse the elements of a stream.

$stream->reverse(): Stream

use IterTools\Stream;

$words = ['are', 'you', 'as' ,'bored', 'as', 'I', 'am'];

$reversed = Stream::of($words)
    ->reverse()
    ->toString(' ');
// am I as bored as you are

Running Average

Return a stream accumulating the running average (mean) over the stream.

$stream->runningAverage(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, 3, 5];

$result = Stream::of($input)
    ->runningAverage()
    ->toArray();
// 1, 2, 3

Running Difference

Return a stream accumulating the running difference over the stream.

$stream->runningDifference(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->runningDifference()
    ->toArray();
// -1, -3, -6, -10, -15

Running Max

Return a stream accumulating the running max over the stream.

$stream->runningMax(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($input)
    ->runningMax()
    ->toArray();
// 1, 1, 2, 2, 3, 3

Running Min

Return a stream accumulating the running min over the stream.

$stream->runningMin(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($input)
    ->runningMin()
    ->toArray();
// 1, -1, -1, -2, -2, -3

Running Product

Return a stream accumulating the running product over the stream.

$stream->runningProduct(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->runningProduct()
    ->toArray();
// 1, 2, 6, 24, 120

Running Total

Return a stream accumulating the running total over the stream.

$stream->runningTotal(int|float|null $initialValue = null): Stream

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->runningTotal()
    ->toArray();
// 1, 3, 6, 10, 15

Skip

Skip some elements of the stream.

$stream->skip(int $count, int $offset = 0): Stream

use IterTools\Stream;

$movies = [
    'The Phantom Menace', 'Attack of the Clones', 'Revenge of the Sith',
    'A New Hope', 'The Empire Strikes Back', 'Return of the Jedi',
    'The Force Awakens', 'The Last Jedi', 'The Rise of Skywalker'
];

$onlyTheBest = Stream::of($movies)
    ->skip(3)
    ->skip(3, 3)
    ->toArray();
// 'A New Hope', 'The Empire Strikes Back', 'Return of the Jedi'

Slice

Extract a slice of the stream.

$stream->slice(int $start = 0, int $count = null, int $step = 1)

use IterTools\Stream;

$olympics = [1992, 1994, 1996, 1998, 2000, 2002, 2004, 2006, 2008, 2010, 2012, 2014, 2016, 2018, 2020, 2022];

$summerOlympics = Stream::of($olympics)
    ->slice(0, 8, 2)
    ->toArray();
// [1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020]

Sort

Sorts the stream.

$stream->sort(callable $comparator = null)

If comparator is not provided, the elements of the iterable source must be comparable.

use IterTools\Stream;

$input = [3, 4, 5, 9, 8, 7, 1, 6, 2];

$result = Stream::of($input)
    ->sort()
    ->toArray();
// 1, 2, 3, 4, 5, 6, 7, 8, 9

Symmetric difference With

Return a stream of the symmetric difference of the stream and the given iterables.

$stream->symmetricDifferenceWith(iterable ...$iterables): Stream

Note: If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Stream;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

$stream = Stream::of($a)
    ->symmetricDifferenceWith($b, $c)
    ->toArray();
// '1', 4, 5, 6, 7, 8, 9

Symmetric difference Coercive With

Return a stream of the symmetric difference of the stream and the given iterables using type coercion.

$stream->symmetricDifferenceCoerciveWith(iterable ...$iterables): Stream

Note: If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Stream;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

$stream = Stream::of($a)
    ->symmetricDifferenceCoerciveWith($b, $c)
    ->toArray();
// 4, 5, 6, 7, 8, 9

Take While

Keep elements from the stream as long as the predicate is true.

$stream->takeWhile(callable $predicate): Stream

If no predicate is provided, the boolean value of the data is used.

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($input)
    ->takeWhile(fn ($value) => abs($value) < 3)
    ->toArray();
// 1, -1, 2, -2

Union With

Return a stream consisting of the union of the stream and the input iterables.

$stream->unionWith(iterable ...$iterables): Stream

Note: If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Stream;

$input = [1, 2, 3];

$stream = Stream::of($input)
    ->unionWith([3, 4, 5, 6])
    ->toArray();
// [1, 2, 3, 4, 5, 6]

Union Coercive With

Return a stream consisting of the union of the stream and the input iterables using type coercion.

$stream->unionCoerciveWith(iterable ...$iterables): Stream

Note: If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Stream;

$input = [1, 2, 3];

$stream = Stream::of($input)
    ->unionCoerciveWith(['3', 4, 5, 6])
    ->toArray();
// [1, 2, 3, 4, 5, 6]

Zip With

Return a stream consisting of multiple iterable collections streamed simultaneously.

$stream->zipWith(iterable ...$iterables): Stream

For uneven lengths, iterations stops when the shortest iterable is exhausted.

use IterTools\Stream;

$input = [1, 2, 3];

$stream = Stream::of($input)
    ->zipWith([4, 5, 6])
    ->zipWith([7, 8, 9])
    ->toArray();
// [1, 4, 7], [2, 5, 8], [3, 6, 9]

Zip Filled With

Return a stream consisting of multiple iterable collections, using a default filler value if lengths no equal.

$stream->zipFilledWith(mixed $default, iterable ...$iterables): Stream

use IterTools\Stream;

$input = [1, 2, 3];

$stream = Stream::of($input)
    ->zipFilledWith('?', ['A', 'B']);

foreach ($stream as $zipped) {
    // [1, A], [2, B], [3, ?]
}

Zip Equal With

Return a stream consisting of multiple iterable collections of equal lengths streamed simultaneously.

$stream->zipEqualWith(iterable ...$iterables): Stream

Works like Stream::zipWith() method but throws \LengthException if lengths not equal, i.e., at least one iterator ends before the others.

use IterTools\Stream;

$input = [1, 2, 3];

$stream = Stream::of($input)
    ->zipEqualWith([4, 5, 6])
    ->zipEqualWith([7, 8, 9]);

foreach ($stream as $zipped) {
    // [1, 4, 7], [2, 5, 8], [3, 6, 9]
}

Zip Longest With

Return a stream consisting of multiple iterable collections streamed simultaneously.

$stream->zipLongestWith(iterable ...$iterables): Stream

Iteration continues until the longest iterable is exhausted.
For uneven lengths, the exhausted iterables will produce null for the remaining iterations.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$stream = Stream::of($input)
    ->zipLongestWith([4, 5, 6])
    ->zipLongestWith([7, 8, 9, 10]);

foreach ($stream as $zipped) {
    // [1, 4, 7], [2, 5, 8], [3, 6, 9], [4, null, 10], [null, null, 5]
}

Stream Terminal Operations

Stream Summary Terminal Operations

All Match

Returns true if all elements match the predicate function.

$stream->allMatch(callable $predicate): bool

use IterTools\Summary;

$finalFantasyNumbers = [4, 5, 6];
$isOnSuperNintendo   = fn ($ff) => $ff >= 4 && $ff <= 6;

$boolean = Stream::of($finalFantasyNumbers)
    ->allMatch($isOnSuperNintendo);
// true

All Unique

Returns true if all elements are unique.

$stream->allUnique(bool $strict = true): bool

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Summary;

$items = ['fingerprints', 'snowflakes', 'eyes', 'DNA']

$boolean = Stream::of($items)
    ->allUnique();
// true

Any Match

Returns true if any element matches the predicate function.

$stream->anyMatch(callable $predicate): bool

use IterTools\Summary;

$answers          = ['fish', 'towel', 42, "don't panic"];
$isUltimateAnswer = fn ($a) => a == 42;

$boolean = Stream::of($answers)
    ->anyMatch($answers, $isUltimateAnswer);
// true

Are Permutations With

Returns true if all iterables are permutations with stream.

$stream->arePermutationsWith(...$iterables): bool

use IterTools\Summary;

$rite = ['r', 'i', 't', 'e'];
$reit = ['r', 'e', 'i', 't'];
$tier = ['t', 'i', 'e', 'r'];
$tire = ['t', 'i', 'r', 'e'];
$trie = ['t', 'r', 'i', 'e'];

$boolean = Stream::of(['i', 't', 'e', 'r'])
    ->arePermutationsWith($rite, $reit, $tier, $tire, $trie);
// true

Are Permutations Coercive With

Returns true if all iterables are permutations with stream with type coercion.

$stream->arePermutationsCoerciveWith(...$iterables): bool

use IterTools\Summary;

$set2 = [2.0, '1', 3];
$set3 = [3, 2, 1];

$boolean = Stream::of([1, 2.0, '3'])
    ->arePermutationsCoerciveWith($set2, $set3);
// true

Exactly N

Returns true if exactly n items are true according to a predicate function.

Predicate is optional.
Default predicate is boolean value of each item.

$stream->exactlyN(int $n, callable $predicate = null): bool

use IterTools\Summary;

$twoTruthsAndALie = [true, true, false];
$n                = 2;

$boolean = Stream::of($twoTruthsAndALie)->exactlyN($n);
// true

Is Empty

Returns true if the stream is empty having no items.

$stream->isEmpty(): bool

use IterTools\Summary;

$numbers    = [0, 1, 2, 3, 4, 5];
$filterFunc = fn ($x) => $x > 10;

$boolean = Stream::($numbers)
    ->filter($filterFunc)
    ->isEmpty();
// true

Is Partitioned

Returns true if all elements of given collection that satisfy the predicate appear before all elements that don't.

Returns true for empty collection or for collection with single item.
Default predicate if not provided is the boolean value of each data item.

$stream->isPartitioned(callable $predicate = null): bool

use IterTools\Summary;

$numbers          = [0, 2, 4, 1, 3, 5];
$evensBeforeOdds = fn ($item) => $item % 2 === 0;

$boolean = Stream::($numbers)
    ->isPartitioned($evensBeforeOdds);
// true

Is Sorted

Returns true if iterable source is sorted in ascending order; otherwise false.

$stream->isSorted(): bool

Items of iterable source must be comparable.

Returns true if iterable source is empty or has only one element.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->isSorted();
// true

$input = [1, 2, 3, 2, 1];

$result = Stream::of($input)
    ->isSorted();
// false

Is Reversed

Returns true if iterable source is sorted in reverse descending order; otherwise false.

$stream->isReversed(): bool

Items of iterable source must be comparable.

Returns true if iterable source is empty or has only one element.

use IterTools\Stream;

$input = [5, 4, 3, 2, 1];

$result = Stream::of($input)
    ->isReversed();
// true

$input = [1, 2, 3, 2, 1];

$result = Stream::of($input)
    ->isReversed();
// false

None Match

Returns true if no element matches the predicate function.

$stream->noneMatch(callable $predicate): bool

use IterTools\Summary;

$grades         = [45, 50, 61, 0];
$isPassingGrade = fn ($grade) => $grade >= 70;

$boolean = Stream::of($grades)->noneMatch($isPassingGrade);
// true

Same With

Returns true if iterable source and all given collections are the same.

$stream->sameWith(iterable ...$iterables): bool

For empty iterables list returns true.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->sameWith([1, 2, 3, 4, 5]);
// true

$result = Stream::of($input)
    ->sameWith([5, 4, 3, 2, 1]);
// false

Same Count With

Returns true if iterable source and all given collections have the same lengths.

$stream->sameCountWith(iterable ...$iterables): bool

For empty iterables list returns true.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($input)
    ->sameCountWith([5, 4, 3, 2, 1]);
// true

$result = Stream::of($input)
    ->sameCountWith([1, 2, 3]);
// false

Stream Reduction Terminal Operations

To Average

Reduces iterable source to the mean average of its items.

$stream->toAverage(): mixed

Returns null if iterable source is empty.

use IterTools\Stream;

$input = [2, 4, 6, 8];

$result = Stream::of($iterable)
    ->toAverage();
// 5

To Count

Reduces iterable source to its length.

$stream->toCount(): mixed

use IterTools\Stream;

$input = [10, 20, 30, 40, 50];

$result = Stream::of($iterable)
    ->toCount();
// 5

To First

Reduces iterable source to its first element.

$stream->toFirst(): mixed

Throws \LengthException if iterable source is empty.

use IterTools\Stream;

$input = [10, 20, 30];

$result = Stream::of($input)
    ->toFirst();
// 10

To First And Last

Reduces iterable source to its first and last elements.

$stream->toFirstAndLast(): array{mixed, mixed}

Throws \LengthException if iterable source is empty.

use IterTools\Stream;

$input = [10, 20, 30];

$result = Stream::of($input)
    ->toFirstAndLast();
// [10, 30]

To Last

Reduces iterable source to its last element.

$stream->toLast(): mixed

Throws \LengthException if iterable source is empty.

use IterTools\Stream;

$input = [10, 20, 30];

$result = Stream::of($input)
    ->toLast();
// 30

To Max

Reduces iterable source to its max value.

$stream->toMax(callable $compareBy = null): mixed

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns null if collection is empty.

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($iterable)
    ->toMax();
// 3

To Min

Reduces iterable source to its min value.

$stream->toMin(callable $compareBy = null): mixed

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns null if collection is empty.

use IterTools\Stream;

$input = [1, -1, 2, -2, 3, -3];

$result = Stream::of($iterable)
    ->toMin();
// -3

To Min Max

Reduces stream to array of its upper and lower bounds (max and min).

$stream->toMinMax(callable $compareBy = null): array

Optional callable param $compareBy must return comparable value.
If $compareBy is not provided then items of given collection must be comparable.
Returns [null, null] if given collection is empty.

use IterTools\Stream;

$numbers = [1, 2, 7, -1, -2, -3];

[$min, $max] = Stream::of($numbers)
    ->toMinMax();
// [-3, 7]

To Nth

Reduces stream to value at the nth position.

$stream->toNth(int $position): mixed

Returns null if iterable source is empty.

use IterTools\Stream;

$lotrMovies = ['The Fellowship of the Ring', 'The Two Towers', 'The Return of the King'];

$result = Stream::of($lotrMovies)
    ->toNth(2);
// The Return of the King

To Product

Reduces stream to the product of its items.

$stream->toProduct(): mixed

Returns null if iterable source is empty.

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($iterable)
    ->toProduct();
// 120

To Random Value

Reduces stream to a random value within it.

$stream->toRandomValue(): mixed

use IterTools\Stream;

$rpsHands = ['rock', 'paper', 'scissors']

$range = Stream::of($numbers)
    ->map('strtoupper')
    ->toRandomValue();
// e.g., rock

To Range

Reduces stream to its range (difference between max and min).

$stream->toRange(): int|float

Returns 0 if iterable source is empty.

use IterTools\Stream;

$grades = [100, 90, 80, 85, 95];

$range = Stream::of($numbers)
    ->toRange();
// 20

To String

Reduces to a string joining all elements.

Optional separator to insert between items.
Optional prefix to prepend to the string.
Optional suffix to append to the string.

$stream->toString(string $separator = '', string $prefix = '', string $suffix = ''): string

use IterTools\Stream;

$words = ['IterTools', 'PHP', 'v1.0'];

$string = Stream::of($words)->toString($words);
// IterToolsPHPv1.0
$string = Stream::of($words)->toString($words, '-');
// IterTools-PHP-v1.0
$string = Stream::of($words)->toString($words, '-', 'Library: ');
// Library: IterTools-PHP-v1.0
$string = Stream::of($words)->toString($words, '-', 'Library: ', '!');
// Library: IterTools-PHP-v1.0!

To Sum

Reduces iterable source to the sum of its items.

$stream->toSum(): mixed

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($iterable)
    ->toSum();
// 15

To Value

Reduces iterable source like array_reduce() function.

But unlike array_reduce(), it works with all iterable types.

$stream->toValue(callable $reducer, mixed $initialValue): mixed

use IterTools\Stream;

$input = [1, 2, 3, 4, 5];

$result = Stream::of($iterable)
    ->toValue(fn ($carry, $item) => $carry + $item);
// 15

Transformation Terminal Operations

To Array

Returns an array of stream elements.

$stream->toArray(): array

use IterTools\Stream;

$array = Stream::of([1, 1, 2, 2, 3, 4, 5])
    ->distinct()
    ->map(fn ($x) => $x**2)
    ->toArray();
// [1, 4, 9, 16, 25]

To Associative Array

Returns a key-value map of stream elements.

$stream->toAssociativeArray(callable $keyFunc, callable $valueFunc): array

use IterTools\Stream;

$keyFunc

$array = Stream::of(['message 1', 'message 2', 'message 3'])
    ->map('strtoupper')
    ->toAssociativeArray(
        fn ($s) => \md5($s),
        fn ($s) => $s
    );
// [3b3f2272b3b904d342b2d0df2bf31ed4 => MESSAGE 1, 43638d919cfb8ea31979880f1a2bb146 => MESSAGE 2, ... ]

Tee

Return several independent (duplicated) streams.

$stream->tee(int $count): array

use IterTools\Transform;

$daysOfWeek = ['Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat', 'Sun'];
$count = 3;

[$week1Stream, $week2Stream, $week3Stream] = Stream::of($daysOfWeek)
    ->tee($count);

// Each $weekStream contains ['Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat', 'Sun']

Side Effect Terminal Operations

Call For Each

Perform an action via a callable on each item in the stream.

$stream->callForEach(callable $function): void

use IterTools\Stream;

$languages = ['PHP', 'Python', 'Java', 'Go'];
$mascots   = ['elephant', 'snake', 'bean', 'gopher'];

$zipPrinter = fn ($zipped) => print("{$zipped[0]}'s mascot: {$zipped[1]}");

Stream::of($languages)
    ->zipWith($mascots)
    ->callForEach($zipPrinter);
// PHP's mascot: elephant
// Python's mascot: snake
// ...

Print

Prints each item in the stream.

Items must be printable.

$stream->print(string $separator = '', string $prefix = '', string $suffix = ''): void

use IterTools\Stream;

$words = ['IterTools', 'PHP', 'v1.0'];

Stream::of($words)->print();                       // IterToolsPHPv1.0
Stream::of($words)->print('-');                    // IterTools-PHP-v1.0
Stream::of($words)->print('-', 'Library: ');       // Library: IterTools-PHP-v1.0
Stream::of($words)->print('-', 'Library: ', '!');  // Library: IterTools-PHP-v1.0!

Print Line

Prints each item in the stream on its own line.

Items must be printable.

$stream->println(): void

use IterTools\Stream;

$words = ['IterTools', 'PHP', 'v1.0'];

Stream::of($words)->printLn();
// IterTools
// PHP
// v1.0

To CSV File

Write the contents of the stream to a CSV file.

$stream->toCsvFile(resource $fileHandle, array $header = null, string 'separator = ',', string $enclosure = '"', string $escape = '\\'): void

use IterTools\Stream;

$starWarsMovies = [
    ['Star Wars: Episode IV – A New Hope', 'IV', 1977],
    ['Star Wars: Episode V – The Empire Strikes Back', 'V', 1980],
    ['Star Wars: Episode VI – Return of the Jedi', 'VI', 1983],
];
$header = ['title', 'episode', 'year'];

Stream::of($data)
    ->toCsvFile($fh, $header);
// title,episode,year
// "Star Wars: Episode IV – A New Hope",IV,1977
// "Star Wars: Episode V – The Empire Strikes Back",V,1980
// "Star Wars: Episode VI – Return of the Jedi",VI,1983

To File

Write the contents of the stream to a file.

$stream->toFile(resource $fileHandle, string $newLineSeparator = \PHP_EOL, string $header = null, string $footer = null): void

use IterTools\Stream;

$data = ['item1', 'item2', 'item3'];
$header = '<ul>';
$footer = '</ul>';

Stream::of($data)
    ->map(fn ($item) => "  <li>$item</li>")
    ->toFile($fh, \PHP_EOL, $header, $footer);

// <ul>
//   <li>item1</li>
//   <li>item2</li>
//   <li>item3</li>
// </ul>

Stream Debug Operations

Peek

Peek at each element between other Stream operations to do some action without modifying the stream.

$stream->peek(callable $callback): Stream

use IterTools\Stream;

$logger = new SimpleLog\Logger('/tmp/log.txt', 'iterTools');

Stream::of(['some', 'items'])
  ->map('strtoupper')
  ->peek(fn ($x) => $logger->info($x))
  ->foreach($someComplexCallable);

Peek Stream

Peek at the entire stream between other Stream operations to do some action without modifying the stream.

$stream->peekStream(callable $callback): Stream

use IterTools\Stream;

$logger = new SimpleLog\Logger('/tmp/log.txt', 'iterTools');

Stream::of(['some', 'items'])
  ->map('strtoupper')
  ->peekStream(fn ($stream) => $logger->info($stream))
  ->foreach($someComplexCallable);

Peek Print

Peek at each element between other Stream operations to print each item without modifying the stream.

$stream->peekPrint(string $separator = '', string $prefix = '', string $suffix = ''): void

use IterTools\Stream;

Stream::of(['some', 'items'])
  ->map('strtoupper')
  ->peekPrint()
  ->foreach($someComplexCallable);

Peek PrintR

Peek at each element between other Stream operations to print_r each item without modifying the stream.

$stream->peekPrintR(callable $callback): void

use IterTools\Stream;

Stream::of(['some', 'items'])
  ->map('strtoupper')
  ->peekPrintR()
  ->foreach($someComplexCallable);

Print R

print_r each item in the stream.

$stream->printR(): void

use IterTools\Stream;

$items = [$string, $array, $object];

Stream::of($words)->printR();
// print_r output

Var Dump

var_dump each item in the stream.

$stream->varDump(): void

use IterTools\Stream;

$items = [$string, $array, $object];

Stream::of($words)->varDump();
// var_dump output

Composition

IterTools can be combined to create new iterable compositions.

Zip Strings

use IterTools\Multi;
use IterTools\Single;

$letters = 'ABCDEFGHI';
$numbers = '123456789';

foreach (Multi::zip(Single::string($letters), Single::string($numbers)) as [$letter, $number]) {
     $battleshipMove = new BattleshipMove($letter, $number)
}
// A1, B2, C3

Chain Strings

use IterTools\Multi;
use IterTools\Single;

$letters = 'abc';
$numbers = '123';

foreach (Multi::chain(Single::string($letters), Single::string($numbers)) as $character) {
    print($character);
}
// a, b, c, 1, 2, 3

Strict and Coercive Types

When there is an option, the default will do strict type comparisons:

scalars: compares strictly by type
objects: always treats different instances as not equal to each other
arrays: compares serialized

When type coercion (non-strict types) is available and enabled via optional flag:

scalars: compares by value via type juggling
objects: compares serialized
arrays: compares serialized

Standards

IterTools PHP conforms to the following standards:

PSR-1 - Basic coding standard (http://www.php-fig.org/psr/psr-1/)
PSR-4 - Autoloader (http://www.php-fig.org/psr/psr-4/)
PSR-12 - Extended coding style guide (http://www.php-fig.org/psr/psr-12/)

License

IterTools PHP is licensed under the MIT License.

Similar Libraries in Other Languages

IterTools functionality is not limited to PHP and Python. Other languages have similar libraries. Familiar functionality is available when working in other languages.

IterTools TypeScript/Javascript
IterTools Python: The original!

Files

README.md

Latest commit

History

README.md

File metadata and controls

IterTools - PHP Iteration Tools to Power Up Your Loops

Features

README docs translated in other languages:

Quick Reference

Loop Iteration Tools

Multi Iteration

Single Iteration

Infinite Iteration

Random Iteration

Math Iteration

Set and multiset Iteration

Sort Iteration

File Iteration

Transform Iteration

Summary

Reduce

Stream Iteration Tools

Stream Sources

Stream Operations

Stream Terminal Operations

Summary Terminal Operations

Reduction Terminal Operations

Transformation Terminal Operations

Side Effect Terminal Operations

Stream Debug Operations

Setup

Minimum Requirements

Usage

Multi Iteration

Chain

Zip

ZipEqual

ZipFilled

ZipLongest

Single Iteration

Chunkwise

Chunkwise Overlap

Compress

Compress Associative

Drop While

Filter

Filter True

Filter False

Filter Keys

Flat Map

Flatten

Group By

Limit

Map

Pairwise

Repeat

Reindex

Reverse

Skip

Slice

String

Take While

Infinite Iteration

Count

Cycle

Repeat (Infinite)

Random Iteration

Choice

CoinFlip

Number

Percentage

RockPaperScissors

Math Iteration

Frequencies

Relative Frequencies

Running Average

Running Difference

Running Max

Running Min