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

Groups in parallel the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function.

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

public static ParallelQuery<IGrouping<TKey, TElement>> GroupBy<TSource, TKey, TElement>(
	this ParallelQuery<TSource> source,
	Func<TSource, TKey> keySelector,
	Func<TSource, TElement> elementSelector,
	IEqualityComparer<TKey> comparer
)

Type Parameters

TSource

The type of elements of source.

TKey

The type of the key returned by keySelector.

TElement

The type of the elements in the IGrouping

Parameters

source
Type: System.Linq.ParallelQuery<TSource>

An OrderedParallelQuery{TSource}that contains elements to sort.

keySelector
Type: System.Func<TSource, TKey>

A function to extract a key from an element.

elementSelector
Type: System.Func<TSource, TElement>

A function to map each source element to an element in an IGrouping.

comparer
Type: System.Collections.Generic.IEqualityComparer<TKey>

An IComparer{TSource} to compare keys.

Return Value

Type: System.Linq.ParallelQuery<IGrouping<TKey, TElement>>
A sequence of groups that are sorted descending according to TKey.

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: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

.NET for Windows Phone apps

Supported in: Windows Phone 8.1

Portable Class Library

Supported in: Portable Class Library
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