Array.Sort<T> Method (T[], Comparison<T>)

Sorts the elements in an Array using the specified Comparison<T>.

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

public static void Sort<T>(
	T[] array,
	Comparison<T> comparison
)

Type Parameters

T

The type of the elements of the array.

Parameters

array
Type: T[]

The one-dimensional, zero-based Array to sort

comparison
Type: System.Comparison<T>

The Comparison<T> to use when comparing elements.

ExceptionCondition
ArgumentNullException

array is null.

-or-

comparison is null.

ArgumentException

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

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

This method uses the 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.

On average, this method is an O(n log n) operation, where n is the Length of array; in the worst case it is an O(n ^ 2) operation.

The following code example demonstrates the Sort(Comparison<T>) method overload.

The code example defines an alternative comparison method for strings, named CompareDinosByLength. This method works as follows: First, the comparands are tested for null, and a null reference is treated as less than a non-null. Second, the string lengths are compared, and the longer string is deemed to be greater. Third, if the lengths are equal, ordinary string comparison is used.

A array of strings is created and populated with four strings, in no particular order. The list also includes an empty string and a null reference. The list is displayed, sorted using a Comparison<T> generic delegate representing the CompareDinosByLength method, and displayed again.

using System;
using System.Collections.Generic;

public class Example
{
    private static int CompareDinosByLength(string x, string y)
    {
        if (x == null)
        {
            if (y == null)
            {
                // If x is null and y is null, they're 
                // equal.  
                return 0;
            }
            else
            {
                // If x is null and y is not null, y 
                // is greater.  
                return -1;
            }
        }
        else
        {
            // If x is not null... 
            // 
            if (y == null)
                // ...and y is null, x is greater.
            {
                return 1;
            }
            else
            {
                // ...and y is not null, compare the  
                // lengths of the two strings. 
                // 
                int retval = x.Length.CompareTo(y.Length);

                if (retval != 0)
                {
                    // If the strings are not of equal length, 
                    // the longer string is greater. 
                    // 
                    return retval;
                }
                else
                {
                    // If the strings are of equal length, 
                    // sort them with ordinary string comparison. 
                    // 
                    return x.CompareTo(y);
                }
            }
        }
    }

    public static void Main()
    {
        string[] dinosaurs = {
            "Pachycephalosaurus",
            "Amargasaurus",
            "",
            null,
            "Mamenchisaurus",
            "Deinonychus" };
        Display(dinosaurs);

        Console.WriteLine("\nSort with generic Comparison<string> delegate:");
        Array.Sort(dinosaurs, CompareDinosByLength);
        Display(dinosaurs);

    }

    private static void Display(string[] arr)
    {
        Console.WriteLine();
        foreach( string s in arr )
        {
            if (s == null)
                Console.WriteLine("(null)");
            else
                Console.WriteLine("\"{0}\"", s);
        }
    }
}

/* This code example produces the following output:

"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"

Sort with generic Comparison<string> delegate:

(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
 */

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
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