GroupBy(TSource, TKey, TElement) Method (ParallelQuery(TSource), Func(TSource, TKey), Func(TSource, TElement), IEqualityComparer(TKey))

Task Parallel System.Threading

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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
Assembly: System.Threading (in System.Threading.dll)

Syntax

Visual Basic (Declaration)
Public Shared Function GroupBy(Of TSource, TKey, TElement) ( _ source As ParallelQuery(Of TSource), _ keySelector As Func(Of TSource, TKey), _ elementSelector As Func(Of TSource, TElement), _ comparer As IEqualityComparer(Of TKey) _ ) As ParallelQuery(Of IGrouping(Of TKey, TElement))

Visual Basic (Declaration)

Public Shared Function GroupBy(Of TSource, TKey, TElement) ( _
	source As ParallelQuery(Of TSource), _
	keySelector As Func(Of TSource, TKey), _
	elementSelector As Func(Of TSource, TElement), _
	comparer As IEqualityComparer(Of TKey) _
) As ParallelQuery(Of IGrouping(Of TKey, TElement))

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

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

Parameters

source: Type: System.Linq..::.ParallelQuery<(Of <(TSource>)>)
An OrderedParallelQuery{TSource}than contains elements to sort.

keySelector: Type: System..::.Func<(Of <(TSource, TKey>)>)
A function to extract a key from an element.

elementSelector: Type: System..::.Func<(Of <(TSource, TElement>)>)
A function to map each source element to an element in an IGrouping.

comparer: Type: System.Collections.Generic..::.IEqualityComparer<(Of <(TKey>)>)
An IComparer{TSource} to compare keys.

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

Return Value

A ParallelQuery{IGrouping{TKey, TElement}} in C# or ParallelQuery(Of IGrouping(Of TKey, TElement)) in Visual Basic where each IGrouping generic object contains a collection of objects of type TElement and a key.

Exceptions

Exception	Condition
System..::.ArgumentNullException	source or keySelector or elementSelector is a null reference (Nothing in Visual Basic).