GroupBy(TSource, TKey, TResult) Method (IEnumerable(TSource), Func(TSource, TKey), Func(TKey, IEnumerable(TSource), TResult), IEqualityComparer(TKey))

Enumerable.GroupBy<TSource, TKey, TResult> Method (IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, IEnumerable<TSource>, TResult>, IEqualityComparer<TKey>)

 

Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The keys are compared by using a specified comparer.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

public static IEnumerable<TResult> GroupBy<TSource, TKey, TResult>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	Func<TKey, IEnumerable<TSource>, TResult> resultSelector,
	IEqualityComparer<TKey> comparer
)

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> whose elements to group.

keySelector
Type: System.Func<TSource, TKey>

A function to extract the key for each element.

resultSelector
Type: System.Func<TKey, IEnumerable<TSource>, TResult>

A function to create a result value from each group.

comparer
Type: System.Collections.Generic.IEqualityComparer<TKey>

An IEqualityComparer<T> to compare keys with.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>

A collection of elements of type TResult where each element represents a projection over a group and its key.

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

TResult

The type of the result value returned by resultSelector.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
Show:
© 2016 Microsoft