Array.Sort<'TKey, 'TValue> Method ('TKey[], 'TValue[], IComparer<'TKey>)


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Sorts a pair of Array objects (one contains the keys and the other contains the corresponding items) based on the keys in the first Array using the specified IComparer<'T> generic interface.

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

static member Sort<'TKey, 'TValue> : 
        keys:'TKey[] *
        items:'TValue[] *
        comparer:IComparer<'TKey> -> unit


Type: 'TKey[]

The one-dimensional, zero-based Array that contains the keys to sort.

Type: 'TValue[]

The one-dimensional, zero-based Array that contains the items that correspond to the keys in keys, or null to sort only keys.

Type: System.Collections.Generic.IComparer<'TKey>

The IComparer<'T> generic interface implementation to use when comparing elements, or null to use the IComparable<'T> generic interface implementation of each element.

Type Parameters


The type of the elements of the key array.


The type of the elements of the items array.

Exception Condition

keys is null.


items is not null, and the lower bound of keys does not match the lower bound of items.


items is not null, and the length of keys is greater than the length of items.


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


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

Each key in the keysArray has a corresponding item in the itemsArray. When a key is repositioned during the sorting, the corresponding item in the itemsArray is similarly repositioned. Therefore, the itemsArray is sorted according to the arrangement of the corresponding keys in the keysArray.

If comparer is null, each key in the keysArray must implement the IComparable<'T> generic interface to be capable of comparisons with every other key.

You can sort if there are more items than keys, but the items that have no corresponding keys will not be sorted. You cannot sort if there are more keys than items; doing this throws an ArgumentException.

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.

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<'TKey, 'TValue>('TKey[], 'TValue[]), Sort<'TKey, 'TValue>('TKey[], 'TValue[], IComparer<'TKey>),Sort<'TKey, 'TValue>('TKey[], 'TValue[], Int32, Int32), and Sort<'TKey, 'TValue>('TKey[], 'TValue[], Int32, Int32, IComparer<'TKey>) generic method overloads, for sorting pairs of arrays that represent keys and values.

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 (the keys) and an array of integers representing the maximum length of each dinosaur in meters (the values). The arrays are then sorted and displayed several times:


The calls to the 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 two arguments. 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.

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

Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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