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ArrayList.Sort Method (IComparer)

Updated: October 2008

Sorts the elements in the entire ArrayList using the specified comparer.

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

'Declaration
Public Overridable Sub Sort ( _
	comparer As IComparer _
)
'Usage
Dim instance As ArrayList 
Dim comparer As IComparer

instance.Sort(comparer)

Parameters

comparer
Type: System.Collections.IComparer

The IComparer implementation to use when comparing elements.

-or-

Nothing to use the IComparable implementation of each element.

ExceptionCondition
NotSupportedException

The ArrayList is read-only.

If comparer is set to Nothing, this method performs a comparison sort (also called 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. To perform a stable sort, you must implement a custom IComparer interface.

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 code example shows how to sort the values in an ArrayList using the default comparer and a custom comparer that reverses the sort order.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList

   Public Class myReverserClass
      Implements IComparer

      ' Calls CaseInsensitiveComparer.Compare with the parameters reversed. 
      Public Function Compare( ByVal x As Object, ByVal 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 ArrayList. 
      Dim myAL As New ArrayList()
      myAL.Add("The")
      myAL.Add("quick")
      myAL.Add("brown")
      myAL.Add("fox")
      myAL.Add("jumps")
      myAL.Add("over")
      myAL.Add("the")
      myAL.Add("lazy")
      myAL.Add("dog")

      ' Displays the values of the ArrayList.
      Console.WriteLine("The ArrayList initially contains the following values:")
      PrintIndexAndValues(myAL)

      ' Sorts the values of the ArrayList using the default comparer.
      myAL.Sort()
      Console.WriteLine("After sorting with the default comparer:")
      PrintIndexAndValues(myAL)

      ' Sorts the values of the ArrayList using the reverse case-insensitive comparer. 
      Dim myComparer = New myReverserClass()
      myAL.Sort(myComparer)
      Console.WriteLine("After sorting with the reverse case-insensitive comparer:")
      PrintIndexAndValues(myAL)

   End Sub 'Main

   Public Shared Sub PrintIndexAndValues(myList As IEnumerable)
      Dim i As Integer = 0
      Dim obj As [Object]
      For Each obj In  myList
         Console.WriteLine(vbTab + "[{0}]:" + vbTab + "{1}", i, obj)
         i = i + 1
      Next obj
      Console.WriteLine()
   End Sub 'PrintIndexAndValues

End Class 'SamplesArrayList


'This code produces the following output. 
'The ArrayList initially contains the following values: 
'        [0]:    The 
'        [1]:    quick 
'        [2]:    brown 
'        [3]:    fox 
'        [4]:    jumps 
'        [5]:    over 
'        [6]:    the 
'        [7]:    lazy 
'        [8]:    dog 

'After sorting with the default comparer: 
'        [0]:    brown 
'        [1]:    dog 
'        [2]:    fox 
'        [3]:    jumps 
'        [4]:    lazy 
'        [5]:    over 
'        [6]:    quick 
'        [7]:    the 
'        [8]:    The 

'After sorting with the reverse case-insensitive comparer: 
'        [0]:    the 
'        [1]:    The 
'        [2]:    quick 
'        [3]:    over 
'        [4]:    lazy 
'        [5]:    jumps 
'        [6]:    fox 
'        [7]:    dog 
'        [8]:    brown

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

October 2008

Revised the Remarks section to note that the QuickSort algorithm is a comparison sort.

Information enhancement.

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