Export (0) Print
Expand All

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 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.

The .NET Framework includes predefined IComparer implementations listed in the following table.

Implementation

Description

System.Collections.CaseInsensitiveComparer

Compares any two objects, but performs a case-insensitive comparison of strings.

Comparer.Default

Compares any two objects by using the sorting conventions of the current culture.

Comparer.DefaultInvariant

Compares any two objects by using the sorting conventions of the invariant culture.

Comparer<T>.Default

Compares two objects of type T by using the type's default sort order.

You can also support custom comparisons by providing an instance of your own IComparer implementation to the comparer parameter. The example does this by defining a ReverseComparer class that reverses the default sort order for instances of a type and performs case-insensitive string comparison.

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 example sorts the values in a string array by using the default comparer. It also defines a custom IComparer implementation named ReverseComparer that reverses an object's default sort order while performing a case-insensitive string comparison. Note that the output might vary depending on the current culture.

using System;
using System.Collections;

public class ReverseComparer : IComparer  
{
   // Call CaseInsensitiveComparer.Compare with the parameters reversed. 
   public int Compare(Object x, Object y)  
   {
       return (new CaseInsensitiveComparer()).Compare(y, x );
   }
}

public class Example 
{
   public static void Main()  
   {
      // Create and initialize a new array. 
      String[] words = { "The", "QUICK", "BROWN", "FOX", "jumps", 
                         "over", "the", "lazy", "dog" };
      // Instantiate the reverse comparer.
      IComparer revComparer = new ReverseComparer();

      // Display the values of the array.
      Console.WriteLine( "The original order of elements in the array:" );
      DisplayValues(words);

      // Sort a section of the array using the default comparer.
      Array.Sort(words, 1, 3);
      Console.WriteLine( "After sorting elements 1-3 by using the default comparer:");
      DisplayValues(words);

      // Sort a section of the array using the reverse case-insensitive comparer.
      Array.Sort(words, 1, 3, revComparer);
      Console.WriteLine( "After sorting elements 1-3 by using the reverse case-insensitive comparer:");
      DisplayValues(words);

      // Sort the entire array using the default comparer.
      Array.Sort(words);
      Console.WriteLine( "After sorting the entire array by using the default comparer:");
      DisplayValues(words);

      // Sort the entire array by using the reverse case-insensitive comparer.
      Array.Sort(words, revComparer);
      Console.WriteLine( "After sorting the entire array using the reverse case-insensitive comparer:");
      DisplayValues(words);
   }

   public static void DisplayValues(String[] arr)  
   {
      for ( int i = arr.GetLowerBound(0); i <= arr.GetUpperBound(0);
            i++ )  {
         Console.WriteLine( "   [{0}] : {1}", i, arr[i] );
      }
      Console.WriteLine();
   }
}
// The example displays the following output: 
//    The original order of elements in the array: 
//       [0] : The 
//       [1] : QUICK 
//       [2] : BROWN 
//       [3] : FOX 
//       [4] : jumps 
//       [5] : over 
//       [6] : the 
//       [7] : lazy 
//       [8] : dog 
//     
//    After sorting elements 1-3 by using the default comparer: 
//       [0] : The 
//       [1] : BROWN 
//       [2] : FOX 
//       [3] : QUICK 
//       [4] : jumps 
//       [5] : over 
//       [6] : the 
//       [7] : lazy 
//       [8] : dog 
//     
//    After sorting elements 1-3 by 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 by 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, 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 Silverlight 8.1, Windows Phone Silverlight 8

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.

Show:
© 2014 Microsoft