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


Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.

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

static member GroupBy<'TSource, 'TKey, 'TResult> : 
        source:IEnumerable<'TSource> *
        keySelector:Func<'TSource, 'TKey> *
        resultSelector:Func<'TKey, IEnumerable<'TSource>, 'TResult> -> IEnumerable<'TResult>


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

An IEnumerable<'T> whose elements to group.

Type: System.Func<'TSource, 'TKey>

A function to extract the key for each element.

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

A function to create a result value from each group.

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


The type of the elements of source.


The type of the key returned by keySelector.


The type of the result value returned by resultSelector.

In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy.

The following code example demonstrates how to use GroupBy<'TSource, 'TKey, 'TResult>(IEnumerable<'TSource>, Func<'TSource, 'TKey>, Func<'TKey, IEnumerable<'TSource>, 'TResult>) to group the elements of a sequence and project a sequence of results of type TResult.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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