Enumerable::GroupBy<TSource, TKey, TElement, TResult> Method (IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, Func<TKey, IEnumerable<TElement>, 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. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.

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

[ExtensionAttribute]
public:
generic<typename TSource, typename TKey, typename TElement, typename TResult>
static IEnumerable<TResult>^ GroupBy(
	IEnumerable<TSource>^ source, 
	Func<TSource, TKey>^ keySelector, 
	Func<TSource, TElement>^ elementSelector, 
	Func<TKey, IEnumerable<TElement>^, TResult>^ resultSelector, 
	IEqualityComparer<TKey>^ comparer
)

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

TElement

The type of the elements in each IGrouping<TKey, TElement>.

TResult

The type of the result value returned by resultSelector.

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.

elementSelector
Type: System::Func<TSource, TElement>

A function to map each source element to an element in an IGrouping<TKey, TElement>.

resultSelector
Type: System::Func<TKey, IEnumerable<TElement>, 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.

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).

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2015 Microsoft