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Array.Sort<T> Method (T[], Int32, Int32, IComparer<T>)

Sorts the elements in a range of elements in an Array using the specified IComparer<T> generic interface.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
public static void Sort<T>(
	T[] array,
	int index,
	int length,
	IComparer<T> comparer
)

Type Parameters

T

The type of the elements of the array.

Parameters

array
Type: T[]

The one-dimensional, zero-based Array to sort.

index
Type: System.Int32

The starting index of the range to sort.

length
Type: System.Int32

The number of elements in the range to sort.

comparer
Type: System.Collections.Generic.IComparer<T>

The IComparer<T> generic interface implementation to use when comparing elements, or null to use the IComparable<T> generic interface implementation of each element.

ExceptionCondition
ArgumentNullException

array is null.

ArgumentOutOfRangeException

index is less than the lower bound of array.

-or-

length is less than zero.

ArgumentException

index and length do not specify a valid range in array.

-or-

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

InvalidOperationException

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

If comparer is null, each element within the specified range of elements in array must implement the IComparable<T> generic 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 length.

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 demonstrates the Sort<T>(T[], Int32, Int32) generic method overload and the Sort<TKey, TValue>(TKey[], TValue[], Int32, Int32, IComparer<TKey>) generic method overload for sorting a range in an array.

The code example defines an alternative comparer for strings, named ReverseCompare, which implements the IComparer<string> (IComparer(Of String) in Visual Basic, IComparer<String^> in Visual C++) generic interface. The comparer calls the CompareTo(String) method, reversing the order of the comparands so that the strings sort high-to-low instead of low-to-high.

The code example creates and displays an array of dinosaur names, consisting of three herbivores followed by three carnivores (tyrannosaurids, to be precise). The Sort<T>(T[], Int32, Int32) generic method overload is used to sort the last three elements of the array, which is then displayed. The Sort<TKey, TValue>(TKey[], TValue[], Int32, Int32, IComparer<TKey>) generic method overload is used with ReverseCompare to sort the last three elements in reverse order. The thoroughly confused dinosaurs are displayed again.

NoteNote

The calls to the Sort<T>(T[], IComparer<T>) and BinarySearch<T>(T[], T, IComparer<T>) generic methods do not look any different from calls to their nongeneric counterparts, because Visual Basic, C#, and C++ infer the type of the generic type parameter from the type of the first argument. If you use the Ildasm.exe (IL Disassembler) to examine the Microsoft intermediate language (MSIL), you can see that the generic methods are being called.

using System;
using System.Collections.Generic;

public class ReverseComparer: IComparer<string>
{
    public int Compare(string x, string y)
    {
        // Compare y and x in reverse order. 
        return y.CompareTo(x);
    }
}

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = {"Pachycephalosaurus", 
                              "Amargasaurus", 
                              "Mamenchisaurus", 
                              "Tarbosaurus",
                              "Tyrannosaurus", 
                              "Albertasaurus"};

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nSort(dinosaurs, 3, 3)");
        Array.Sort(dinosaurs, 3, 3);

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }

        ReverseComparer rc = new ReverseComparer();

        Console.WriteLine("\nSort(dinosaurs, 3, 3, rc)");
        Array.Sort(dinosaurs, 3, 3, rc);

        Console.WriteLine();
        foreach( string dinosaur in dinosaurs )
        {
            Console.WriteLine(dinosaur);
        }
    }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Tarbosaurus
Tyrannosaurus
Albertasaurus

Sort(dinosaurs, 3, 3)

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Albertasaurus
Tarbosaurus
Tyrannosaurus

Sort(dinosaurs, 3, 3, rc)

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Tyrannosaurus
Tarbosaurus
Albertasaurus
 */

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.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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