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List(T).Sort Method (IComparer(T))

Sorts the elements in the entire List(T) using the specified comparer.

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

member Sort : 
        comparer:IComparer<'T> -> unit


Type: System.Collections.Generic.IComparer(T)

The IComparer(T) implementation to use when comparing elements, or a null reference (Nothing in Visual Basic) to use the default comparer Comparer(T).Default.


comparer is a null reference (Nothing in Visual Basic), and the default comparer Comparer(T).Default cannot find implementation of the IComparable(T) generic interface or the IComparable interface for type T.


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 provided, the elements of the List(T) are sorted using the specified IComparer(T) implementation.

If comparer is a null reference (Nothing in Visual Basic), the default comparer Comparer(T).Default checks whether type T implements the IComparable(T) generic interface and uses that implementation, if available. If not, Comparer(T).Default checks whether type T implements the IComparable interface. If type T does not implement either interface, Comparer(T).Default throws an InvalidOperationException.

This method uses the Array.Sort method, which applies the introspective sort 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.

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

The following example demonstrates the Sort(IComparer(T)) method overload and the BinarySearch(T, IComparer(T)) method overload.

The example defines an alternative comparer for strings named DinoCompare, which implements the IComparer<string> (IComparer(Of String) in Visual Basic, IComparer<String^> in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for a null reference (Nothing in Visual Basic), 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 List(T) of strings is created and populated with four strings, in no particular order. The list is displayed, sorted using the alternate comparer, and displayed again.

The BinarySearch(T, IComparer(T)) method overload is then used to search for several strings that are not in the list, employing the alternate comparer. The Insert method is used to insert the strings. These two methods are located in the function named SearchAndInsert, along with code to take the bitwise complement (the ~ operator in C# and Visual C++, Xor -1 in Visual Basic) of the negative number returned by BinarySearch(T, IComparer(T)) and use it as an index for inserting the new string.

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

.NET Framework

Supported in: 4.5.2, 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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