Enumerable.GroupBy(Of TSource, TKey, TElement, TResult) Method (IEnumerable(Of TSource), Func(Of TSource, TKey), Func(Of TSource, TElement), Func(Of TKey, IEnumerable(Of TElement), TResult), IEqualityComparer(Of 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
Assembly:  System.Core (in System.Core.dll)

'Declaration
<ExtensionAttribute> _
Public Shared Function GroupBy(Of TSource, TKey, TElement, TResult) ( _
	source As IEnumerable(Of TSource), _
	keySelector As Func(Of TSource, TKey), _
	elementSelector As Func(Of TSource, TElement), _
	resultSelector As Func(Of TKey, IEnumerable(Of TElement), TResult), _
	comparer As IEqualityComparer(Of TKey) _
) As IEnumerable(Of TResult)

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(Of TKey, TElement).

TResult

The type of the result value returned by resultSelector.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) whose elements to group.
keySelector
Type: System.Func(Of TSource, TKey)
A function to extract the key for each element.
elementSelector
Type: System.Func(Of TSource, TElement)
A function to map each source element to an element in an IGrouping(Of TKey, TElement).
resultSelector
Type: System.Func(Of TKey, IEnumerable(Of TElement), TResult)
A function to create a result value from each group.
comparer
Type: System.Collections.Generic.IEqualityComparer(Of TKey)
An IEqualityComparer(Of T) to compare keys with.

Return Value

Type: System.Collections.Generic.IEnumerable(Of 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(Of TSource). When you use instance method syntax to call this method, omit the first parameter.

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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