Array.Sort<T> Method (array<T[], IComparer<T>)

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Sorts the elements in an Array using the specified IComparer<T> generic interface.

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

Syntax

'Declaration
Public Shared Sub Sort(Of T) ( _
    array As T(), _
    comparer As IComparer(Of T) _
)

public static void Sort<T>(
    T[] array,
    IComparer<T> comparer
)

Type Parameters

• T
  The type of the elements of the array.

Parameters

• array
  Type: array<T[]
  The one-dimensional, zero-base Array to sort

• comparer
  Type: System.Collections.Generic.IComparer<T>
  The IComparer<T> generic interface implementation to use when comparing elements, or nulla null reference (Nothing in Visual Basic) to use the IComparable<T> generic interface implementation of each element.

Exceptions

Exception	Condition
ArgumentNullException	array is nulla null reference (Nothing in Visual Basic).
InvalidOperationException	comparer is nulla null reference (Nothing in Visual Basic), and one or more elements in array do not implement the IComparable<T> generic interface.
ArgumentException	The implementation of comparer caused an error during the sort. For example, comparer might not return 0 when comparing an item with itself.

Remarks

If comparer is nulla null reference (Nothing in Visual Basic), each element of array must implement the IComparable<T> generic 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 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 the Length of array; in the worst case it is an O(n ^ 2) operation.

Examples

The following code example demonstrates the Sort<T>(array<T[], IComparer<T>) generic method overload and the BinarySearch<T>(array<T[], T, IComparer<T>) generic method overload.

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 array is displayed, sorted, and displayed again. Arrays must be sorted in order to use the BinarySearch method.

Note:
The calls to the Sort<T>(array<T[], IComparer<T>) and BinarySearch<T>(array<T[], T, IComparer<T>) 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 argument.

The BinarySearch<T>(array<T[], T, IComparer<T>) generic method overload is then used to search for two strings, one that is not in the array and one that is. The array and the return value of the BinarySearch<T>(array<T[], T, IComparer<T>) method are passed to the ShowWhere generic method, which displays the index value if the string is found, and otherwise the elements the search string would fall between if it were in the array. The index is negative if the string is not n the array, so the ShowWhere method takes the bitwise complement (the ~ operator in C# and Visual C++, Xor -1 in Visual Basic) to obtain the index of the first element in the list that is larger than the search string.

Imports System.Collections.Generic

Public Class ReverseComparer
   Implements IComparer(Of String)

   Public Function Compare(ByVal x As String, _
       ByVal y As String) As Integer _
       Implements IComparer(Of String).Compare

      ' Compare y and x in reverse order.
      Return y.CompareTo(x)

   End Function
End Class

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim dinosaurs() As String = { _
          "Pachycephalosaurus", _
          "Amargasaurus", _
          "Tyrannosaurus", _
          "Mamenchisaurus", _
          "Deinonychus", _
          "Edmontosaurus"}

      outputBlock.Text &= vbCrLf
      For Each dinosaur As String In dinosaurs
         outputBlock.Text &= dinosaur & vbCrLf
      Next

      Dim rc As New ReverseComparer()

      outputBlock.Text &= vbLf & "Sort" & vbCrLf
      Array.Sort(dinosaurs, rc)

      outputBlock.Text &= vbCrLf
      For Each dinosaur As String In dinosaurs
         outputBlock.Text &= dinosaur & vbCrLf
      Next

      outputBlock.Text &= vbLf & _
          "BinarySearch for 'Coelophysis':" & vbCrLf
      Dim index As Integer = _
          Array.BinarySearch(dinosaurs, "Coelophysis", rc)
      ShowWhere(outputBlock, dinosaurs, index)

      outputBlock.Text &= vbLf & _
          "BinarySearch for 'Tyrannosaurus':" & vbCrLf
      index = Array.BinarySearch(dinosaurs, "Tyrannosaurus", rc)
      ShowWhere(outputBlock, dinosaurs, index)

   End Sub

   Private Shared Sub ShowWhere(Of T) _
       (ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal array() As T, ByVal index As Integer)

      If index < 0 Then
         ' If the index is negative, it represents the bitwise
         ' complement of the next larger element in the array.
         '
         index = index Xor -1

         outputBlock.Text &= "Not found. Sorts between: "

         If index = 0 Then
            outputBlock.Text &= "beginning of array and "
         Else
            outputBlock.Text &= String.Format("{0} and ", array(index - 1))
         End If

         If index = array.Length Then
            outputBlock.Text &= "end of array." & vbCrLf
         Else
            outputBlock.Text &= String.Format("{0}.", array(index)) & vbCrLf
         End If
      Else
         outputBlock.Text &= String.Format("Found at index {0}.", index) & vbCrLf
      End If

   End Sub

End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Amargasaurus
'Tyrannosaurus
'Mamenchisaurus
'Deinonychus
'Edmontosaurus
'
'Sort
'
'Tyrannosaurus
'Pachycephalosaurus
'Mamenchisaurus
'Edmontosaurus
'Deinonychus
'Amargasaurus
'
'BinarySearch for 'Coelophysis':
'Not found. Sorts between: Deinonychus and Amargasaurus.
'
'BinarySearch for 'Tyrannosaurus':
'Found at index 0.

using System;
using System.Collections.Generic;

public class ReverseComparer : IComparer<string>
{
   public int Compare(string x, string y)
   {
      // Compare y and x in reverse order.
      return y.CompareTo(x);
   }
}

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string[] dinosaurs = {"Pachycephalosaurus", 
                              "Amargasaurus", 
                              "Tyrannosaurus", 
                              "Mamenchisaurus", 
                              "Deinonychus", 
                              "Edmontosaurus"};

      outputBlock.Text += "\n";
      foreach (string dinosaur in dinosaurs)
      {
         outputBlock.Text += dinosaur + "\n";
      }

      ReverseComparer rc = new ReverseComparer();

      outputBlock.Text += "\nSort" + "\n";
      Array.Sort(dinosaurs, rc);

      outputBlock.Text += "\n";
      foreach (string dinosaur in dinosaurs)
      {
         outputBlock.Text += dinosaur + "\n";
      }

      outputBlock.Text += "\nBinarySearch for 'Coelophysis':" + "\n";
      int index = Array.BinarySearch(dinosaurs, "Coelophysis", rc);
      ShowWhere(outputBlock, dinosaurs, index);

      outputBlock.Text += "\nBinarySearch for 'Tyrannosaurus':" + "\n";
      index = Array.BinarySearch(dinosaurs, "Tyrannosaurus", rc);
      ShowWhere(outputBlock, dinosaurs, index);
   }

   private static void ShowWhere<T>(System.Windows.Controls.TextBlock outputBlock, T[] array, int index)
   {
      if (index < 0)
      {
         // If the index is negative, it represents the bitwise
         // complement of the next larger element in the array.
         //
         index = ~index;

         outputBlock.Text += "Not found. Sorts between: ";

         if (index == 0)
            outputBlock.Text += "beginning of array and ";
         else
            outputBlock.Text += String.Format("{0} and ", array[index - 1]);

         if (index == array.Length)
            outputBlock.Text += "end of array." + "\n";
         else
            outputBlock.Text += String.Format("{0}.", array[index]) + "\n";
      }
      else
      {
         outputBlock.Text += String.Format("Found at index {0}.", index) + "\n";
      }
   }
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Tyrannosaurus
Mamenchisaurus
Deinonychus
Edmontosaurus

Sort

Tyrannosaurus
Pachycephalosaurus
Mamenchisaurus
Edmontosaurus
Deinonychus
Amargasaurus

BinarySearch for 'Coelophysis':
Not found. Sorts between: Deinonychus and Amargasaurus.

BinarySearch for 'Tyrannosaurus':
Found at index 0.
 */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

See Also

Reference

Array Class

Sort Overload

System Namespace

IComparer<T>

IComparable<T>

BinarySearch