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MSDN Library

ParallelEnumerable.ToLookup(TSource, TKey, TElement) Method (ParallelQuery(TSource), Func(TSource, TKey), Func(TSource, TElement))

Creates an ILookup(TKey, TElement) from a ParallelQuery(TSource) according to specified key selector and element selector functions.

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

static member ToLookup : 
        source:ParallelQuery<'TSource> * 
        keySelector:Func<'TSource, 'TKey> * 
        elementSelector:Func<'TSource, 'TElement> -> ILookup<'TKey, 'TElement> 

Type Parameters

TSource

The type of elements of source.

TKey

The type of the key returned by keySelector.

TElement

The type of the value returned by elementSelector.

Parameters

source
Type: System.Linq.ParallelQuery(TSource)

The sequence to create a ILookup(TKey, TElement) from.

keySelector
Type: System.Func(TSource, TKey)

A function to extract a key from each element.

elementSelector
Type: System.Func(TSource, TElement)

A transform function to produce a result element value from each element.

Return Value

Type: System.Linq.ILookup(TKey, TElement)
A ILookup(TKey, TElement) that contains values of type TElement selected from the input sequence.

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 keySelector or elementSelector 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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