Article
11/18/2011

Enumerable.Reverse<TSource> Method

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Inverts the order of the elements in a sequence.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Reverse(Of TSource) ( _
    source As IEnumerable(Of TSource) _
) As IEnumerable(Of TSource)

public static IEnumerable<TSource> Reverse<TSource>(
    this IEnumerable<TSource> source
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
A sequence of values to reverse.

Return Value

Type: System.Collections.Generic.IEnumerable<TSource>
A sequence whose elements correspond to those of the input sequence in reverse order.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source is nulla null reference (Nothing in Visual Basic).

Remarks

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

Unlike OrderBy, this sorting method does not consider the actual values themselves in determining the order. Rather, it just returns the elements in the reverse order from which they are produced by the underlying source.

Examples

The following code example demonstrates how to use Reverse<TSource> to reverse the order of elements in an array.

      ' Create a List of Char values.
      Dim appleLetters As New List(Of Char)(New Char() _
                                            {"a"c, "P"c, "P"c, "L"c, "E"c})

      ' Reverse the order of the elements in the list.
      ' (We have to call AsEnumerable() in order to
      ' use System.Linq.Enumerable's Reverse() method.
      Dim reversed() As Char = _
          appleLetters.AsEnumerable().Reverse().ToArray()

      Dim output As New System.Text.StringBuilder
      For Each chr As Char In reversed
         output.Append(chr & " ")
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:
      '
      ' E L P P a

      char[] apple = { 'a', 'p', 'p', 'l', 'e' };

      char[] reversed = apple.Reverse().ToArray();

      foreach (char chr in reversed)
      {
         outputBlock.Text += chr + " ";
      }
      outputBlock.Text += "\n";

      /*
       This code produces the following output:

       e l p p a
      */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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