Add Duplicates Operator

Docs/SuperLinq.Docs/apidoc/SuperLinq.SuperEnumerable.Duplicates.md

@@ -0,0 +1,6 @@
+---
+uid: SuperLinq.SuperEnumerable.Duplicates``1(System.Collections.Generic.IEnumerable{``0},System.Collections.Generic.IEqualityComparer{``0})
+example: [*content]
+---
+The following code example demonstrates how to get the duplicated elements of a sequence using `Duplicates`.
+[!code-csharp[](SuperLinq/Duplicates/Duplicates.linq#L6-)]

Docs/SuperLinq.Docs/apidoc/SuperLinq/Duplicates/Duplicates.linq

@@ -0,0 +1,17 @@
+<Query Kind="Statements">
+  <NuGetReference>SuperLinq</NuGetReference>
+  <Namespace>SuperLinq</Namespace>
+</Query>
+
+var sequence = new[] { "foo", "bar", "baz", "foo", };
+
+// determine if a sequence has duplicate items
+var result = sequence.Duplicates();
+
+Console.WriteLine(
+	"[" +
+	string.Join(", ", result) +
+	"]");
+
+// This code produces the following output:
+// [foo]

README.md

@@ -72,6 +72,7 @@ equivalent elements within the same or separate collections (or sets).
 | Method Name        | Description | Sync doc | Async doc |
 | -----------        | --- | --- | --- |
 | DistinctBy         | Removes duplicate values from a collection. | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.SuperEnumerable.DistinctBy.html) | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.Async.AsyncSuperEnumerable.DistinctBy.html) |
+| Duplicates	     | Returns the sequence of elements that are in the source sequence more than once. | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.SuperEnumerable.Duplicates.html) | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.Async.AsyncSuperEnumerable.Duplicates.html) |
 | ExceptBy	         | Returns the set difference, which means the elements of one collection that do not appear in a second collection. | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.SuperEnumerable.ExceptBy.html) | [link](https://viceroypenguin.github.io/SuperLinq/api/SuperLinq.Async.AsyncSuperEnumerable.ExceptBy.html) |
 
 </details>

Source/SuperLinq.Async/Duplicates.cs

@@ -0,0 +1,55 @@
+namespace SuperLinq.Async;
+
+public static partial class AsyncSuperEnumerable
+{
+	/// <summary>
+	///	    Returns all duplicate elements of the given source.
+	/// </summary>
+	/// <typeparam name="TSource">
+	///	    The type of the elements in the source sequence.
+	/// </typeparam>
+	/// <param name="source">
+	///	    The source sequence.
+	/// </param>
+	/// <param name="comparer">
+	///	    The equality comparer to use to determine whether one <typeparamref name="TSource"/> equals another. If <see
+	///     langword="null"/>, the default equality comparer for <typeparamref name="TSource"/> is used.
+	/// </param>
+	/// <returns>
+	///	    All elements that are duplicated.
+	/// </returns>
+	/// <exception cref="ArgumentNullException">
+	///	    <paramref name="source"/> is <see langword="null"/>.
+	/// </exception>
+	/// <remarks>
+	///	    This operator uses deferred execution and streams its results.
+	/// </remarks>
+	public static IAsyncEnumerable<TSource> Duplicates<TSource>(this IAsyncEnumerable<TSource> source, IEqualityComparer<TSource>? comparer = null)
+	{
+		ArgumentNullException.ThrowIfNull(source);
+
+		comparer ??= EqualityComparer<TSource>.Default;
+
+		return Core(source, comparer);
+
+		static async IAsyncEnumerable<TSource> Core(
+			IAsyncEnumerable<TSource> source,
+			IEqualityComparer<TSource> comparer,
+			[EnumeratorCancellation] CancellationToken token = default)
+		{
+			var counts = new Collections.NullKeyDictionary<TSource, int>(comparer);
+			await foreach (var element in source.WithCancellation(token).ConfigureAwait(false))
+			{
+				if (!counts.TryGetValue(element, out var count))
+				{
+					counts[element] = 1;
+				}
+				else if (count == 1)
+				{
+					yield return element;
+					counts[element] = 2;
+				}
+			}
+		}
+	}
+}

Source/SuperLinq.Async/HasDuplicates.cs

@@ -62,22 +62,9 @@ public static ValueTask<bool> HasDuplicates<TSource, TKey>(this IAsyncEnumerable
 		ArgumentNullException.ThrowIfNull(source);
 		ArgumentNullException.ThrowIfNull(keySelector);
 
-		return Core(source, keySelector, comparer);
-
-		static async ValueTask<bool> Core(IAsyncEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer)
-		{
-			var enumeratedElements = new HashSet<TKey>(comparer);
-
-			await foreach (var element in source.ConfigureAwait(false))
-			{
-				if (!enumeratedElements.Add(keySelector(element)))
-				{
-					return true;
-				}
-			}
-
-			return false;
-		}
+		return source
+			.Select(keySelector)
+			.Duplicates(comparer)
+			.AnyAsync();
 	}
 }
-

Source/SuperLinq.Async/PublicAPI/net6.0/PublicAPI.Unshipped.txt

@@ -1,6 +1,7 @@
 #nullable enable
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.Async.AsyncSuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<TSource>!
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IEnumerable<T>!, System.Collections.Generic.IEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<(System.Collections.Generic.IEnumerable<T>! True, System.Collections.Generic.IEnumerable<T>! False)>
 *REMOVED*static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IAsyncEnumerable<T>!, System.Collections.Generic.IAsyncEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>

Source/SuperLinq.Async/PublicAPI/net7.0/PublicAPI.Unshipped.txt

@@ -1,6 +1,7 @@
 #nullable enable
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.Async.AsyncSuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<TSource>!
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IEnumerable<T>!, System.Collections.Generic.IEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<(System.Collections.Generic.IEnumerable<T>! True, System.Collections.Generic.IEnumerable<T>! False)>
 *REMOVED*static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IAsyncEnumerable<T>!, System.Collections.Generic.IAsyncEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>

Source/SuperLinq.Async/PublicAPI/net8.0/PublicAPI.Unshipped.txt

@@ -1,6 +1,7 @@
 #nullable enable
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.Async.AsyncSuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<TSource>!
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IEnumerable<T>!, System.Collections.Generic.IEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<(System.Collections.Generic.IEnumerable<T>! True, System.Collections.Generic.IEnumerable<T>! False)>
 *REMOVED*static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IAsyncEnumerable<T>!, System.Collections.Generic.IAsyncEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>

Source/SuperLinq.Async/PublicAPI/netcoreapp3.1/PublicAPI.Unshipped.txt

@@ -1,6 +1,7 @@
 #nullable enable
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.Async.AsyncSuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.Async.AsyncSuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IAsyncEnumerable<TSource>!
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IEnumerable<T>!, System.Collections.Generic.IEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>
 static SuperLinq.Async.AsyncSuperEnumerable.Partition<T>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<(System.Collections.Generic.IEnumerable<T>! True, System.Collections.Generic.IEnumerable<T>! False)>
 *REMOVED*static SuperLinq.Async.AsyncSuperEnumerable.Partition<T, TResult>(this System.Collections.Generic.IAsyncEnumerable<T>! source, System.Func<T, bool>! predicate, System.Func<System.Collections.Generic.IAsyncEnumerable<T>!, System.Collections.Generic.IAsyncEnumerable<T>!, TResult>! resultSelector, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.ValueTask<TResult>

Source/SuperLinq/Duplicates.cs

@@ -0,0 +1,52 @@
+namespace SuperLinq;
+
+public static partial class SuperEnumerable
+{
+	/// <summary>
+	///	    Returns all duplicate elements of the given source.
+	/// </summary>
+	/// <typeparam name="TSource">
+	///	    The type of the elements in the source sequence.
+	/// </typeparam>
+	/// <param name="source">
+	///	    The source sequence.
+	/// </param>
+	/// <param name="comparer">
+	///	    The equality comparer to use to determine whether one <typeparamref name="TSource"/> equals another. If <see
+	///     langword="null"/>, the default equality comparer for <typeparamref name="TSource"/> is used.
+	/// </param>
+	/// <returns>
+	///	    All elements that are duplicated.
+	/// </returns>
+	/// <exception cref="ArgumentNullException">
+	///	    <paramref name="source"/> is <see langword="null"/>.
+	/// </exception>
+	/// <remarks>
+	///	    This operator uses deferred execution and streams its results.
+	/// </remarks>
+	public static IEnumerable<TSource> Duplicates<TSource>(this IEnumerable<TSource> source, IEqualityComparer<TSource>? comparer = null)
+	{
+		ArgumentNullException.ThrowIfNull(source);
+
+		comparer ??= EqualityComparer<TSource>.Default;
+
+		return Core(source, comparer);
+
+		static IEnumerable<TSource> Core(IEnumerable<TSource> source, IEqualityComparer<TSource> comparer)
+		{
+			var counts = new Collections.NullKeyDictionary<TSource, int>(comparer);
+			foreach (var element in source)
+			{
+				if (!counts.TryGetValue(element, out var count))
+				{
+					counts[element] = 1;
+				}
+				else if (count == 1)
+				{
+					yield return element;
+					counts[element] = 2;
+				}
+			}
+		}
+	}
+}

Source/SuperLinq/HasDuplicates.cs

@@ -130,18 +130,9 @@ public static bool HasDuplicates<TSource, TKey>(
 		ArgumentNullException.ThrowIfNull(source);
 		ArgumentNullException.ThrowIfNull(keySelector);
 
-		var enumeratedElements = source.TryGetCollectionCount() is { } collectionCount
-			? new HashSet<TKey>(collectionCount, comparer)
-			: new HashSet<TKey>(comparer);
-
-		foreach (var element in source)
-		{
-			if (!enumeratedElements.Add(keySelector(element)))
-			{
-				return true;
-			}
-		}
-
-		return false;
+		return source
+			.Select(keySelector)
+			.Duplicates(comparer)
+			.Any();
 	}
 }

Source/SuperLinq/PublicAPI/net6.0/PublicAPI.Unshipped.txt

@@ -3,4 +3,5 @@
 *REMOVED*static SuperLinq.SuperEnumerable.Share<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<System.Collections.Generic.IEnumerable<TSource>!, System.Collections.Generic.IEnumerable<TResult>!>! selector) -> System.Collections.Generic.IEnumerable<TResult>!
 static SuperLinq.SuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.SuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.SuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IEnumerable<TSource>!
 static SuperLinq.SuperEnumerable.Take<TSource>(System.Collections.Generic.IEnumerable<TSource>! source, System.Range range) -> System.Collections.Generic.IEnumerable<TSource>!

Source/SuperLinq/PublicAPI/net7.0/PublicAPI.Unshipped.txt

@@ -3,4 +3,5 @@
 *REMOVED*static SuperLinq.SuperEnumerable.Share<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<System.Collections.Generic.IEnumerable<TSource>!, System.Collections.Generic.IEnumerable<TResult>!>! selector) -> System.Collections.Generic.IEnumerable<TResult>!
 static SuperLinq.SuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, System.Func<TKey, TAccumulate>! seedSelector, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
 static SuperLinq.SuperEnumerable.AggregateBy<TSource, TKey, TAccumulate>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Func<TSource, TKey>! keySelector, TAccumulate seed, System.Func<TAccumulate, TSource, TAccumulate>! func, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) -> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TAccumulate>>!
+static SuperLinq.SuperEnumerable.Duplicates<TSource>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) -> System.Collections.Generic.IEnumerable<TSource>!
 static SuperLinq.SuperEnumerable.Take<TSource>(System.Collections.Generic.IEnumerable<TSource>! source, System.Range range) -> System.Collections.Generic.IEnumerable<TSource>!