List<T>.Sort Method (Comparison<T>)
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Sorts the elements in the entire List<T> using the specified System.Comparison<T>.
Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Sub Sort ( _
comparison As Comparison(Of T) _
)
public void Sort(
Comparison<T> comparison
)
Parameters
- comparison
Type: System.Comparison<T>
The System.Comparison<T> to use when comparing elements.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | comparison is nulla null reference (Nothing in Visual Basic). |
| ArgumentException | The implementation of comparison caused an error during the sort. For example, comparison might not return 0 when comparing an item with itself. |
Remarks
If comparison is provided, the elements of the List<T> are sorted using the method represented by the delegate.
If comparison is nulla null reference (Nothing in Visual Basic), an ArgumentNullException is thrown.
This method uses Array.Sort, which 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 Count; in the worst case it is an O(n ^ 2) operation.
Examples
The following code example demonstrates the Sort(Comparison<T>) method overload.
The code example defines an alternative comparison method for strings, named CompareDinosByLength. This method works as follows: First, the comparands are tested for nulla 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 also includes an empty string and a null reference. The list is displayed, sorted using a Comparison<T> generic delegate representing the CompareDinosByLength method, and displayed again.
Imports System.Collections.Generic
Public Class Example
Private Shared Function CompareDinosByLength( _
ByVal x As String, ByVal y As String) As Integer
If x Is Nothing Then
If y Is Nothing Then
' If x is Nothing and y is Nothing, they're
' equal.
Return 0
Else
' If x is Nothing and y is not Nothing, y
' is greater.
Return -1
End If
Else
' If x is not Nothing...
'
If y Is Nothing Then
' ...and y is Nothing, x is greater.
Return 1
Else
' ...and y is not Nothing, compare the
' lengths of the two strings.
'
Dim retval As Integer = _
x.Length.CompareTo(y.Length)
If retval <> 0 Then
' If the strings are not of equal length,
' the longer string is greater.
'
Return retval
Else
' If the strings are of equal length,
' sort them with ordinary string comparison.
'
Return x.CompareTo(y)
End If
End If
End If
End Function
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim dinosaurs As New List(Of String)
dinosaurs.Add("Pachycephalosaurus")
dinosaurs.Add("Amargasaurus")
dinosaurs.Add("")
dinosaurs.Add(Nothing)
dinosaurs.Add("Mamenchisaurus")
dinosaurs.Add("Deinonychus")
Display(outputBlock, dinosaurs)
outputBlock.Text &= vbLf & "Sort with generic Comparison(Of String) delegate:" & vbCrLf
dinosaurs.Sort(AddressOf CompareDinosByLength)
Display(outputBlock, dinosaurs)
End Sub
Private Shared Sub Display(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal lis As List(Of String))
outputBlock.Text &= vbCrLf
For Each s As String In lis
If s Is Nothing Then
outputBlock.Text &= "(Nothing)" & vbCrLf
Else
outputBlock.Text += String.Format("""{0}""", s) & vbCrLf
End If
Next
End Sub
End Class
' This code example produces the following output:
'
'"Pachycephalosaurus"
'"Amargasaurus"
'""
'(Nothing)
'"Mamenchisaurus"
'"Deinonychus"
'
'Sort with generic Comparison(Of String) delegate:
'
'(Nothing)
'""
'"Deinonychus"
'"Amargasaurus"
'"Mamenchisaurus"
'"Pachycephalosaurus"
using System;
using System.Collections.Generic;
public class Example
{
private static int CompareDinosByLength(string x, string y)
{
if (x == null)
{
if (y == null)
{
// If x is null and y is null, they're
// equal.
return 0;
}
else
{
// If x is null and y is not null, y
// is greater.
return -1;
}
}
else
{
// If x is not null...
//
if (y == null)
// ...and y is null, x is greater.
{
return 1;
}
else
{
// ...and y is not null, compare the
// lengths of the two strings.
//
int retval = x.Length.CompareTo(y.Length);
if (retval != 0)
{
// If the strings are not of equal length,
// the longer string is greater.
//
return retval;
}
else
{
// If the strings are of equal length,
// sort them with ordinary string comparison.
//
return x.CompareTo(y);
}
}
}
}
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
List<string> dinosaurs = new List<string>();
dinosaurs.Add("Pachycephalosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("");
dinosaurs.Add(null);
dinosaurs.Add("Mamenchisaurus");
dinosaurs.Add("Deinonychus");
Display(outputBlock, dinosaurs);
outputBlock.Text += "\nSort with generic Comparison<string> delegate:" + "\n";
dinosaurs.Sort(CompareDinosByLength);
Display(outputBlock, dinosaurs);
}
private static void Display(System.Windows.Controls.TextBlock outputBlock, List<string> list)
{
outputBlock.Text += "\n";
foreach (string s in list)
{
if (s == null)
outputBlock.Text += "(null)" + "\n";
else
outputBlock.Text += String.Format("\"{0}\"", s) + "\n";
}
}
}
/* This code example produces the following output:
"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"
Sort with generic Comparison<string> delegate:
(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
*/
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