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MoreEnumerable.CountBy<TSource, TKey> Method (IEnumerable<TSource>, Func<TSource, TKey>)

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.

Namespace:  MoreLinq
Assembly:  MoreLinq (in MoreLinq.dll) Version: 2.7.0
Syntax
public static IEnumerable<KeyValuePair<TKey, int>> CountBy<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector
)

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
Source sequence.
keySelector
Type: System.Func<TSource, TKey>
Function that transforms each item of source sequence into a key to be compared against the others.

Type Parameters

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

Return Value

Type: IEnumerable<KeyValuePair<TKey, 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 IEnumerable<TSource>. 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).
See Also