GroupBy(TSource, TKey, TResult) Method (ParallelQuery(TSource), Func(TSource, TKey), Func(TKey, IEnumerable(TSource), TResult), IEqualityComparer(TKey))

Task Parallel System.Threading

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

Syntax

Visual Basic (Declaration)
Public Shared Function GroupBy(Of TSource, TKey, TResult) ( _ source As ParallelQuery(Of TSource), _ keySelector As Func(Of TSource, TKey), _ resultSelector As Func(Of TKey, IEnumerable(Of TSource), TResult), _ comparer As IEqualityComparer(Of TKey) _ ) As ParallelQuery(Of TResult)

Visual Basic (Declaration)

Public Shared Function GroupBy(Of TSource, TKey, TResult) ( _
	source As ParallelQuery(Of TSource), _
	keySelector As Func(Of TSource, TKey), _
	resultSelector As Func(Of TKey, IEnumerable(Of TSource), TResult), _
	comparer As IEqualityComparer(Of TKey) _
) As ParallelQuery(Of TResult)

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

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

Parameters

source: Type: System.Linq..::.ParallelQuery<(Of <(TSource>)>)
A sequence whose elements to group.

keySelector: Type: System..::.Func<(Of <(TSource, TKey>)>)
A function to extract the key for each element.

resultSelector: Type: System..::.Func<(Of <(TKey, IEnumerable<(Of <(TSource>)>), TResult>)>)
A function to create a result value from each group.

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

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.

Return Value

An ParallelQuery<IGrouping<TKey, TResult>> in C# or ParallelQuery(Of IGrouping(Of TKey, TResult)) in Visual Basic where each IGrouping<(Of <(TKey, TResult>)>) object contains a collection of objects of type TResult and a key.

Exceptions

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