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ParallelEnumerable.AsOrdered Method (ParallelQuery)

Enables treatment of a data source as if it was ordered, overriding the default of unordered. AsOrdered may only be invoked on non-generic sequences returned by AsParallel, ParallelEnumerable.Range, and ParallelEnumerable.Repeat.

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

public static ParallelQuery AsOrdered(
	this ParallelQuery source


Type: System.Linq.ParallelQuery
The input sequence.

Return Value

Type: System.Linq.ParallelQuery
The source sequence which will maintain the original ordering in the subsequent query operators.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type ParallelQuery. 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 is a null reference (Nothing in Visual Basic).


thrown if source contains no elements


if AsOrdered is called midway through a query. It is allowed to be called immediately after AsParallel, Range or Repeat<TResult>.

A natural tension exists between performance and preserving order in parallel processing. By default, a parallelized query behaves as if the ordering of the results is arbitrary unless AsOrdered is applied or there is an explicit OrderBy operator in the query. For more information, see Order Preservation in PLINQ.

.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.