Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
Export (0) Print
Expand All

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


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

An IEnumerable<T> whose elements to group.

Type: System.Func<TSourceTKey>

A function to extract the key for each element.

Type: System.Func<TKeyIEnumerable<TSource>, TResult>

A function to create a result value from each group.

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


The type of the elements of source.


The type of the key returned by keySelector.


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
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
Return to top
Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
© 2015 Microsoft