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mapBy2

Apply a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assign results to a strided output array.

Installation

npm install @stdlib/strided-base-map-by2

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var mapBy2 = require( '@stdlib/strided-base-map-by2' );

mapBy2( N, x, strideX, y, strideY, z, strideZ, fcn, clbk[, thisArg] )

Applies a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assigns results to a strided output array.

var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor );
// z => [ -2.0, 4.0, 10.0, -6.0, 14.0, 6.0, 6.0, 2.0 ]

The function accepts the following arguments:

• N: number of indexed elements.
• x: input Array, typed array, or an array-like object (excluding strings and functions).
• strideX: index increment for x.
• y: input Array, typed array, or an array-like object (excluding strings and functions).
• strideY: index increment for y.
• z: output Array, typed array, or an array-like object (excluding strings and functions).
• strideZ: index increment for z.
• fcn: binary function to apply to callback return values.
• clbk: callback function which returns an array-like object containing two values.
• thisArg: execution context (optional).

The invoked callback function is provided four arguments:

• values: input array element values [vx, vy].
• idx: iteration index (zero-based).
• indices: input and output array strided indices [ix, iy, iz] (computed according to offset + idx*stride).
• arrays: input and output arrays/collections [x, y, z].

To set the callback execution context, provide a thisArg.

var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    this.count += 1;
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

var context = {
    'count': 0
};

var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor, context );
// z => [ -2.0, 4.0, 10.0, -6.0, 14.0, 6.0, 6.0, 2.0 ]

var cnt = context.count;
// returns 8

The N and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to index every other value in x and to index the first N elements of y in reverse order,

var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];
var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2( 3, x, 2, y, -1, z, 1, add, accessor );
// z => [ 2.0, -4.0, -8.0, 0.0, 0.0, 0.0 ]

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

var Float64Array = require( '@stdlib/array-float64' );
var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

// Initial arrays...
var x0 = new Float64Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var y0 = new Float64Array( [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ] );
var z0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var z1 = new Float64Array( z0.buffer, z0.BYTES_PER_ELEMENT*2 ); // start at 3rd element

mapBy2( 3, x1, -2, y1, 1, z1, 1, add, accessor );
// z0 => <Float64Array>[ 0.0, 0.0, -8.0, -2.0, 2.0, 0.0 ]

mapBy2.ndarray( N, x, strideX, offsetX, y, strideY, offsetY, z, strideZ, offsetZ, fcn, clbk[, thisArg] )

Applies a binary function to each pair of elements retrieved from strided input arrays according to a callback function and assigns results to a strided output array using alternative indexing semantics.

var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0 ];
var y = [ 1.0, 1.0, 2.0, 2.0, 3.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2.ndarray( x.length, x, 1, 0, y, 1, 0, z, 1, 0, add, accessor );
// z => [ 0.0, -2.0, -2.0, -4.0, -4.0 ]

The function accepts the following additional arguments:

• offsetX: starting index for x.
• offsetY: starting index for y.
• offsetZ: starting index for z.

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to index every other value in x starting from the second value and to index the last N elements in y in reverse order,

var add = require( '@stdlib/math-base-ops-add' );

function accessor( values ) {
    values[ 0 ] *= 2.0;
    values[ 1 ] *= 2.0;
    return values;
}

var x = [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ];
var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0 ];
var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];

mapBy2.ndarray( 3, x, 2, 1, y, -1, y.length-1, z, 1, 3, add, accessor );
// z => [ 0.0, 0.0, 0.0, 2.0, -2.0, -8.0 ]

Notes

• If a provided callback function does not return any value (or equivalently, explicitly returns undefined), the value is ignored.

  var add = require( '@stdlib/math-base-ops-add' );
  
  function accessor() {
      // No-op...
  }
  
  var x = [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ];
  var y = [ 1.0, 1.0, 2.0, 2.0, 3.0, 3.0, 4.0, 4.0 ];
  var z = [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ];
  
  mapBy2( x.length, x, 1, y, 1, z, 1, add, accessor );
  // z => [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ]

Examples

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var filledarray = require( '@stdlib/array-filled' );
var filledarrayBy = require( '@stdlib/array-filled-by' );
var add = require( '@stdlib/math-base-ops-add' );
var mapBy2 = require( '@stdlib/strided-base-map-by2' );

function accessor( values, i ) {
    if ( (i%3) === 0 ) {
        // Simulate a "missing" value...
        return;
    }
    return values;
}

var x = filledarrayBy( 10, 'generic', discreteUniform( -100, 100 ) );
console.log( x );

var y = filledarrayBy( 10, 'generic', discreteUniform( -100, 100 ) );
console.log( y );

var z = filledarray( null, 10, 'generic' );
console.log( z );

mapBy2.ndarray( x.length, x, 1, 0, y, -1, y.length-1, z, 1, 0, add, accessor );
console.log( z );

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See Also

• @stdlib/strided-base/map-by: apply a unary function to each element retrieved from a strided input array according to a callback function and assign results to a strided output array.
• @stdlib/strided-base/binary: apply a binary callback to elements in strided input arrays and assign results to elements in a strided output array.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.