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Enumerable.CountBy<TSource,TKey> Method

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Definition

Namespace:
System.Linq
Assembly:
System.Linq.dll
Source:
CountBy.cs

Returns the count of elements in the source sequence grouped by key.

public static System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,int>> CountBy<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey>? keyComparer = default);
static member CountBy : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IEqualityComparer<'Key> -> seq<System.Collections.Generic.KeyValuePair<'Key, int>>
<Extension()>
Public Function CountBy(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), Optional keyComparer As IEqualityComparer(Of TKey) = Nothing) As IEnumerable(Of KeyValuePair(Of TKey, Integer))

Type Parameters

TSource

The type of elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source
IEnumerable<TSource>

A sequence that contains elements to be counted.

keySelector
Func<TSource,TKey>

A function to extract the key for each element.

keyComparer
IEqualityComparer<TKey>

An IEqualityComparer<T> to compare keys with.

Returns

IEnumerable<KeyValuePair<TKey,Int32>>

An enumerable containing the frequencies of each key occurrence in source.

Applies to