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

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 keys are compared by using a specified comparer.

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

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

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

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.

resultSelector
Type: System.Func<TKey, IEnumerable<TSource>, TResult>

A function to create a result value from each group.

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

An IEqualityComparer<T> to compare keys.

Return Value

Type: System.Linq.ParallelQuery<TResult>
A sequence of groups.

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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