Method Duplicates

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Duplicates<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>?)

Returns all duplicate elements of the given source.

Declaration
public static IEnumerable<TSource> Duplicates<TSource>(this IEnumerable<TSource> source, IEqualityComparer<TSource>? comparer = null)
Parameters
Type Name Description
IEnumerable<TSource> source

The source sequence.
IEqualityComparer<TSource> comparer

The equality comparer to use to determine whether one TSource equals another. If null, the default equality comparer for TSource is used.
Returns
Type Description
IEnumerable<TSource>

All elements that are duplicated.
Type Parameters
Name Description
TSource

The type of the elements in the source sequence.
Remarks

This operator uses deferred execution and streams its results.

Examples

The following code example demonstrates how to get the duplicated elements of a sequence using Duplicates.

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]
Exceptions
Type Condition
ArgumentNullException

source is null.