Array.Sort Method (Array, Array, IComparer)

 

Sorts a pair of one-dimensional 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.

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

Public Shared Sub Sort (
	keys As Array,
	items As Array,
	comparer As IComparer
)

Parameters

keys
Type: System.Array

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

items
Type: System.Array

The one-dimensional Array that contains the items that correspond to each of the keys in the keysArray.

-or-

null to sort only the keysArray.

comparer
Type: System.Collections.IComparer

The IComparer implementation to use when comparing elements.

-or-

null to use the IComparable implementation of each element.

Exception Condition
ArgumentNullException

keys is null.

RankException

The keysArray is multidimensional.

-or-

The itemsArray is multidimensional.

ArgumentException

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

-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 the keysArray do not implement the IComparable 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 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.

The .NET Framework includes predefined IComparer implementations listed in the following table.

Implementation

Description

System.Collections.CaseInsensitiveComparer

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

Comparer.Default

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

Comparer.DefaultInvariant

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

Comparer(Of T).Default

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 an IComparer implementation that reverses the default sort order and performs case-insensitive string comparison.

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 keys.

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 previouslythrew ArgumentException will not throw an exception, becausethe 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 shows how to sort two associated arrays where the first array contains the keys and the second array contains the values. Sorts are done using the default comparer and a custom comparer that reverses the sort order. Note that the result might vary depending on the current CultureInfo.

Imports System
Imports System.Collections

Public Class SamplesArray

   Public Class myReverserClass
      Implements IComparer

      ' Calls CaseInsensitiveComparer.Compare with the parameters reversed.
      Function Compare(x As [Object], y As [Object]) As Integer _
         Implements IComparer.Compare
         Return New CaseInsensitiveComparer().Compare(y, x)
      End Function 'IComparer.Compare

   End Class 'myReverserClass


   Public Shared Sub Main()

      ' Creates and initializes a new Array and a new custom comparer.
      Dim myKeys As [String]() =  {"red", "GREEN", "YELLOW", "BLUE", "purple", "black", "orange"}
      Dim myValues As [String]() =  {"strawberries", "PEARS", "LIMES", "BERRIES", "grapes", "olives", "cantaloupe"}
      Dim myComparer = New myReverserClass()

      ' Displays the values of the Array.
      Console.WriteLine("The Array initially contains the following values:")
      PrintKeysAndValues(myKeys, myValues)

      ' Sorts a section of the Array using the default comparer.
      Array.Sort(myKeys, myValues, 1, 3)
      Console.WriteLine("After sorting a section of the Array using the default comparer:")
      PrintKeysAndValues(myKeys, myValues)

      ' Sorts a section of the Array using the reverse case-insensitive comparer.
      Array.Sort(myKeys, myValues, 1, 3, myComparer)
      Console.WriteLine("After sorting a section of the Array using the reverse case-insensitive comparer:")
      PrintKeysAndValues(myKeys, myValues)

      ' Sorts the entire Array using the default comparer.
      Array.Sort(myKeys, myValues)
      Console.WriteLine("After sorting the entire Array using the default comparer:")
      PrintKeysAndValues(myKeys, myValues)

      ' Sorts the entire Array using the reverse case-insensitive comparer.
      Array.Sort(myKeys, myValues, myComparer)
      Console.WriteLine("After sorting the entire Array using the reverse case-insensitive comparer:")
      PrintKeysAndValues(myKeys, myValues)

   End Sub 'Main


   Public Shared Sub PrintKeysAndValues(myKeys() As [String], myValues() As [String])

      Dim i As Integer
      For i = 0 To myKeys.Length - 1
         Console.WriteLine("   {0,-10}: {1}", myKeys(i), myValues(i))
      Next i
      Console.WriteLine()

   End Sub 'PrintKeysAndValues

End Class 'SamplesArray


'This code produces the following output.
'
'The Array initially contains the following values:
'   red       : strawberries
'   GREEN     : PEARS
'   YELLOW    : LIMES
'   BLUE      : BERRIES
'   purple    : grapes
'   black     : olives
'   orange    : cantaloupe
'
'After sorting a section of the Array using the default comparer:
'   red       : strawberries
'   BLUE      : BERRIES
'   GREEN     : PEARS
'   YELLOW    : LIMES
'   purple    : grapes
'   black     : olives
'   orange    : cantaloupe
'
'After sorting a section of the Array using the reverse case-insensitive comparer:
'   red       : strawberries
'   YELLOW    : LIMES
'   GREEN     : PEARS
'   BLUE      : BERRIES
'   purple    : grapes
'   black     : olives
'   orange    : cantaloupe
'
'After sorting the entire Array using the default comparer:
'   black     : olives
'   BLUE      : BERRIES
'   GREEN     : PEARS
'   orange    : cantaloupe
'   purple    : grapes
'   red       : strawberries
'   YELLOW    : LIMES
'
'After sorting the entire Array using the reverse case-insensitive comparer:
'   YELLOW    : LIMES
'   red       : strawberries
'   purple    : grapes
'   orange    : cantaloupe
'   GREEN     : PEARS
'   BLUE      : BERRIES
'   black     : olives

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Return to top
Show: