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ParallelEnumerable.Select<TSource, TResult> Method (ParallelQuery<TSource>, Func<TSource, Int32, TResult>)

Projects in parallel each element of a sequence into a new form by incorporating the element's index.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

public static ParallelQuery<TResult> Select<TSource, TResult>(
	this ParallelQuery<TSource> source,
	Func<TSource, int, TResult> selector

Type Parameters


The type of the elements of source.


The type of elements resturned by selector.


Type: System.Linq.ParallelQuery<TSource>
A sequence of values to invoke a transform function on.
Type: System.Func<TSource, Int32, TResult>
A transform function to apply to each element.

Return Value

Type: System.Linq.ParallelQuery<TResult>
A sequence whose elements are the result of invoking the transform function on each element of source, based on the index supplied to selector.

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).


source or selector is a null reference (Nothing in Visual Basic).


The query was canceled with the token passed in through WithCancellation.


One or more exceptions occurred during the evaluation of the query.


More than MaxValue elements are enumerated by the query. This condition might occur in streaming scenarios.

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.