CountByExtensionCountByTSource, TKey(IEnumerableTSource, FuncTSource, TKey, IEqualityComparerTKey) Method

Applies a key-generating function to each element of a sequence and returns a sequence of unique keys and their number of occurrences in the original sequence. An additional argument specifies a comparer to use for testing equivalence of keys.

Definition

Namespace: MoreLinq.Extensions
Assembly: MoreLinq (in MoreLinq.dll) Version: 4.4.0+6d97c3b1d482f98300f4446df14742b0e3fafbec

C#

public static IEnumerable<KeyValuePair<TKey, int>> CountBy<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	IEqualityComparer<TKey>? comparer
)

VB

<ExtensionAttribute>
Public Shared Function CountBy(Of TSource, TKey) ( 
	source As IEnumerable(Of TSource),
	keySelector As Func(Of TSource, TKey),
	comparer As IEqualityComparer(Of TKey)
) As IEnumerable(Of KeyValuePair(Of TKey, Integer))

C++

public:
[ExtensionAttribute]
generic<typename TSource, typename TKey>
static IEnumerable<KeyValuePair<TKey, int>>^ CountBy(
	IEnumerable<TSource>^ source, 
	Func<TSource, TKey>^ keySelector, 
	IEqualityComparer<TKey>^ comparer
)

F#

[<ExtensionAttribute>]
static member CountBy : 
        source : IEnumerable<'TSource> * 
        keySelector : Func<'TSource, 'TKey> * 
        comparer : IEqualityComparer<'TKey> -> IEnumerable<KeyValuePair<'TKey, int>>

Parameters

source IEnumerableTSource: Source sequence.
keySelector FuncTSource, TKey: Function that transforms each item of source sequence into a key to be compared against the others.
comparer IEqualityComparerTKey: The equality comparer to use to determine whether or not keys are equal. If null, the default equality comparer for TSource is used.

Type Parameters

TSource: Type of the elements of the source sequence.
TKey: Type of the projected element.

Return Value

IEnumerableKeyValuePairTKey, Int32
A sequence of unique keys and their number of occurrences in the original sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerableTSource. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).