Array.Sort Method (Array, IComparer)


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

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

static member Sort : 
        array:Array *
        comparer:IComparer -> unit


Type: System.Array

The one-dimensional array to sort.

Type: System.Collections.IComparer

The implementation to use when comparing elements.


null to use the IComparable implementation of each element.

Exception Condition

array is null.


array is multidimensional.


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


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.




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


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


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


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 arrayby 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.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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