ParallelEnumerable.ThenByDescending(Of TSource, TKey) Method (OrderedParallelQuery(Of TSource), Func(Of TSource, TKey))

.NET Framework (current version)

Performs in parallel a subsequent ordering of the elements in a sequence in descending order, according to a key.

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

Public Shared Function ThenByDescending(Of TSource, TKey) (
	source As OrderedParallelQuery(Of TSource),
	keySelector As Func(Of TSource, TKey)
) As OrderedParallelQuery(Of TSource)


Type: System.Linq.OrderedParallelQuery(Of TSource)

An OrderedParallelQuery{TSource} that contains elements to sort.

Type: System.Func(Of TSource, TKey)

A function to extract a key from an element.

Return Value

Type: System.Linq.OrderedParallelQuery(Of TSource)

A sequence whose elements are sorted descending according to a key.

Type Parameters


The type of elements of source.


The type of the key returned by keySelector.

Exception Condition

source or keySelector 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.

In contrast to the sequential implementation, this is not a stable sort. See the remarks for OrderBy(Of TSource, TKey) for an approach to implementing a stable sort.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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