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Array.Sort Method (Array, IComparer)

Sorts the elements in a one-dimensional Array using the specified IComparer.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static void Sort(
	Array array,
	IComparer comparer
)

Parameters

array
Type: System.Array

The one-dimensional Array to sort.

comparer
Type: System.Collections.IComparer

The IComparer implementation to use when comparing elements.

-or-

null to use the IComparable implementation of each element.

ExceptionCondition
ArgumentNullException

array is null.

RankException

array is multidimensional.

InvalidOperationException

comparer is null, and one or more elements in array do not implement the IComparable interface.

ArgumentException

The implementation of comparer caused an error during the sort. For example, comparer might not return 0 when comparing an item with itself.

If comparer is null, each element of array must implement the IComparable interface to be capable of comparisons with every other element in array.

If the sort is not successfully completed, the results are undefined.

This method uses the introspective sort (introsort) algorithm as follows:

  • If the partition size is fewer than 16 elements, it uses an insertion sort algorithm.

  • If the number of partitions exceeds 2 * LogN, where N is the range of the input array, it uses a Heapsort algorithm.

  • Otherwise, it uses a Quicksort algorithm.

This implementation performs an unstable sort; that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal.

For arrays that are sorted by using the Heapsort and Quicksort algorithms, in the worst case, this method is an O(n log n) operation, where n is the Length of array.

Notes to Callers

The .NET Framework 4 and earlier versions used only the Quicksort algorithm. Quicksort identifies invalid comparers in some situations in which the sorting operation throws an IndexOutOfRangeException exception, and throws an ArgumentException exception to the caller. Starting with the .NET Framework 4.5, it is possible that sorting operations that previously threw ArgumentException will not throw an exception, because the insertion sort and heapsort algorithms do not detect an invalid comparer. For the most part, this applies to arrays with fewer than 16 elements.

The following code example shows how to sort the values in an Array using the default comparer and a custom comparer that reverses the sort order. Note that the result might vary depending on the current CultureInfo.

using System;
using System.Collections;

public class SamplesArray  {

   public class myReverserClass : IComparer  {

      // Calls CaseInsensitiveComparer.Compare with the parameters reversed. 
      int IComparer.Compare( Object x, Object y )  {
          return( (new CaseInsensitiveComparer()).Compare( y, x ) );
      }

   }

   public static void Main()  {

      // Creates and initializes a new Array and a new custom comparer.
      String[] myArr = { "The", "QUICK", "BROWN", "FOX", "jumps", "over", "the", "lazy", "dog" };
      IComparer myComparer = new myReverserClass();

      // Displays the values of the Array.
      Console.WriteLine( "The Array initially contains the following values:" );
      PrintIndexAndValues( myArr );

      // Sorts a section of the Array using the default comparer.
      Array.Sort( myArr, 1, 3 );
      Console.WriteLine( "After sorting a section of the Array using the default comparer:" );
      PrintIndexAndValues( myArr );

      // Sorts a section of the Array using the reverse case-insensitive comparer.
      Array.Sort( myArr, 1, 3, myComparer );
      Console.WriteLine( "After sorting a section of the Array using the reverse case-insensitive comparer:" );
      PrintIndexAndValues( myArr );

      // Sorts the entire Array using the default comparer.
      Array.Sort( myArr );
      Console.WriteLine( "After sorting the entire Array using the default comparer:" );
      PrintIndexAndValues( myArr );

      // Sorts the entire Array using the reverse case-insensitive comparer.
      Array.Sort( myArr, myComparer );
      Console.WriteLine( "After sorting the entire Array using the reverse case-insensitive comparer:" );
      PrintIndexAndValues( myArr );

   }

   public static void PrintIndexAndValues( String[] myArr )  {
      for ( int i = 0; i < myArr.Length; i++ )  {
         Console.WriteLine( "   [{0}] : {1}", i, myArr[i] );
      }
      Console.WriteLine();
   }
}


/* 
This code produces the following output.

The Array initially contains the following values:
   [0] : The
   [1] : QUICK
   [2] : BROWN
   [3] : FOX
   [4] : jumps
   [5] : over
   [6] : the
   [7] : lazy
   [8] : dog

After sorting a section of the Array using the default comparer:
   [0] : The
   [1] : BROWN
   [2] : FOX
   [3] : QUICK
   [4] : jumps
   [5] : over
   [6] : the
   [7] : lazy
   [8] : dog

After sorting a section of the Array using the reverse case-insensitive comparer:
   [0] : The
   [1] : QUICK
   [2] : FOX
   [3] : BROWN
   [4] : jumps
   [5] : over
   [6] : the
   [7] : lazy
   [8] : dog

After sorting the entire Array using the default comparer:
   [0] : BROWN
   [1] : dog
   [2] : FOX
   [3] : jumps
   [4] : lazy
   [5] : over
   [6] : QUICK
   [7] : the
   [8] : The

After sorting the entire Array using the reverse case-insensitive comparer:
   [0] : the
   [1] : The
   [2] : QUICK
   [3] : over
   [4] : lazy
   [5] : jumps
   [6] : FOX
   [7] : dog
   [8] : BROWN

*/

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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