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ParallelEnumerable.GroupBy<TSource, TKey, TElement, TResult> Method (ParallelQuery<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, Func<TKey, IEnumerable<TElement>, TResult>)

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

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

public static ParallelQuery<TResult> GroupBy<TSource, TKey, TElement, TResult>(
	this ParallelQuery<TSource> source,
	Func<TSource, TKey> keySelector,
	Func<TSource, TElement> elementSelector,
	Func<TKey, IEnumerable<TElement>, TResult> resultSelector
)

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.Linq.ParallelQuery<TSource>
A sequence 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.

Return Value

Type: System.Linq.ParallelQuery<TResult>
A sequence 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 ParallelQuery<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).

ExceptionCondition
OperationCanceledException

The query was canceled with the token passed in through WithCancellation.

ArgumentNullException

source or action is a null reference (Nothing in Visual Basic).

AggregateException

One or more exceptions occurred during the evaluation of the query.

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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