List<T>.SortList<T>.SortList<T>.SortList<T>.Sort Method

Definition

Sorts the elements or a portion of the elements in the List<T> using either the specified or default IComparer<T> implementation or a provided Comparison<T> delegate to compare list elements.

 Sort(Comparison) Sort(Comparison) Sort(Comparison) Sort(Comparison) Sorts the elements in the entire List using the specified Comparison. Sort(Int32, Int32, IComparer) Sort(Int32, Int32, IComparer) Sort(Int32, Int32, IComparer) Sort(Int32, Int32, IComparer) Sorts the elements in a range of elements in List using the specified comparer. Sort() Sort() Sort() Sort() Sorts the elements in the entire List using the default comparer. Sort(IComparer) Sort(IComparer) Sort(IComparer) Sort(IComparer) Sorts the elements in the entire List using the specified comparer.

Sort(Comparison<T>)Sort(Comparison<T>)Sort(Comparison<T>)Sort(Comparison<T>)

Sorts the elements in the entire List<T> using the specified Comparison<T>.

``````public:
void Sort(Comparison<T> ^ comparison);``````
``public void Sort (Comparison<T> comparison);``
``member this.Sort : Comparison<'T> -> unit``
``Public Sub Sort (comparison As Comparison(Of T))``

Parameters

comparison
Comparison<T> Comparison<T> Comparison<T> Comparison<T>

The Comparison<T> to use when comparing elements.

Exceptions

`comparison` is `null`.

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

Examples

The following code demonstrates the Sort and Sort method overloads on a simple business object. Calling the Sort method results in the use of the default comparer for the Part type, and the Sort method is implemented using an anonymous method.

``````using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify the type of part
// but the part name can change.
public class Part : IEquatable<Part> , IComparable<Part>
{
public string PartName { get; set; }

public int PartId { get; set; }

public override string ToString()
{
return "ID: " + PartId + "   Name: " + PartName;
}
public override bool Equals(object obj)
{
if (obj == null) return false;
Part objAsPart = obj as Part;
if (objAsPart == null) return false;
else return Equals(objAsPart);
}
public int SortByNameAscending(string name1, string name2)
{

return name1.CompareTo(name2);
}

// Default comparer for Part type.
public int CompareTo(Part comparePart)
{
// A null value means that this object is greater.
if (comparePart == null)
return 1;

else
return this.PartId.CompareTo(comparePart.PartId);
}
public override int GetHashCode()
{
return PartId;
}
public bool Equals(Part other)
{
if (other == null) return false;
return (this.PartId.Equals(other.PartId));
}
// Should also override == and != operators.

}
public class Example
{
public static void Main()
{
// Create a list of parts.
List<Part> parts = new List<Part>();

// Add parts to the list.
parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
parts.Add(new Part() { PartName= "crank arm", PartId = 1234 });
parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;
// Name intentionally left null.
parts.Add(new Part() {  PartId = 1334 });
parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
parts.Add(new Part() { PartName = "cassette", PartId = 1534 });

// Write out the parts in the list. This will call the overridden
// ToString method in the Part class.
Console.WriteLine("\nBefore sort:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// Call Sort on the list. This will use the
// default comparer, which is the Compare method
// implemented on Part.
parts.Sort();

Console.WriteLine("\nAfter sort by part number:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// This shows calling the Sort(Comparison(T) overload using
// an anonymous method for the Comparison delegate.
// This method treats null as the lesser of two values.
parts.Sort(delegate(Part x, Part y)
{
if (x.PartName == null && y.PartName == null) return 0;
else if (x.PartName == null) return -1;
else if (y.PartName == null) return 1;
else return x.PartName.CompareTo(y.PartName);
});

Console.WriteLine("\nAfter sort by name:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

/*

Before sort:
ID: 1434   Name: regular seat
ID: 1234   Name: crank arm
ID: 1634   Name: shift lever
ID: 1334   Name:
ID: 1444   Name: banana seat
ID: 1534   Name: cassette

After sort by part number:
ID: 1234   Name: crank arm
ID: 1334   Name:
ID: 1434   Name: regular seat
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1634   Name: shift lever

After sort by name:
ID: 1334   Name:
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1234   Name: crank arm
ID: 1434   Name: regular seat
ID: 1634   Name: shift lever

*/

}
}
``````
``````Imports System.Collections.Generic
' Simple business object. A PartId is used to identify the type of part
' but the part name can change.
Public Class Part
Implements IEquatable(Of Part)
Implements IComparable(Of Part)
Public Property PartName() As String
Get
Return m_PartName
End Get
Set(value As String)
m_PartName = Value
End Set
End Property
Private m_PartName As String

Public Property PartId() As Integer
Get
Return m_PartId
End Get
Set(value As Integer)
m_PartId = Value
End Set
End Property
Private m_PartId As Integer

Public Overrides Function ToString() As String
Return "ID: " & PartId & "   Name: " & PartName
End Function

Public Overrides Function Equals(obj As Object) As Boolean
If obj Is Nothing Then
Return False
End If
Dim objAsPart As Part = TryCast(obj, Part)
If objAsPart Is Nothing Then
Return False
Else
Return Equals(objAsPart)
End If
End Function

Public Function SortByNameAscending(name1 As String, name2 As String) As Integer

Return name1.CompareTo(name2)
End Function

' Default comparer for Part.
Public Function CompareTo(comparePart As Part) As Integer _
Implements IComparable(Of ListSortVB.Part).CompareTo
' A null value means that this object is greater.
If comparePart Is Nothing Then
Return 1
Else

Return Me.PartId.CompareTo(comparePart.PartId)
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return PartId
End Function
Public Overloads Function Equals(other As Part) As Boolean Implements IEquatable(Of ListSortVB.Part).Equals
If other Is Nothing Then
Return False
End If
Return (Me.PartId.Equals(other.PartId))
End Function
' Should also override == and != operators.

End Class
Public Class Example
Public Shared Sub Main()
' Create a list of parts.
Dim parts As New List(Of Part)()

' Add parts to the list.
.PartName = "regular seat", _
.PartId = 1434 _
})
.PartName = "crank arm", _
.PartId = 1234 _
})
.PartName = "shift lever", _
.PartId = 1634 _
})

' Name intentionally left null.
.PartId = 1334 _
})
.PartName = "banana seat", _
.PartId = 1444 _
})
.PartName = "cassette", _
.PartId = 1534 _
})

' Write out the parts in the list. This will call the overridden
' ToString method in the Part class.
Console.WriteLine(vbLf & "Before sort:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' Call Sort on the list. This will use the
' default comparer, which is the Compare method
' implemented on Part.
parts.Sort()

Console.WriteLine(vbLf & "After sort by part number:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' This shows calling the Sort(Comparison(T) overload using
' an anonymous delegate method.
' This method treats null as the lesser of two values.
parts.Sort(Function(x As Part, y As Part)
If x.PartName Is Nothing AndAlso y.PartName Is Nothing Then
Return 0
ElseIf x.PartName Is Nothing Then
Return -1
ElseIf y.PartName Is Nothing Then
Return 1
Else
Return x.PartName.CompareTo(y.PartName)
End If
End Function)

Console.WriteLine(vbLf & "After sort by name:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

'
'
'            Before sort:
'            ID: 1434   Name: regular seat
'            ID: 1234   Name: crank arm
'            ID: 1634   Name: shift lever
'            ID: 1334   Name:
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'
'            After sort by part number:
'            ID: 1234   Name: crank arm
'            ID: 1334   Name:
'            ID: 1434   Name: regular seat
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'            ID: 1634   Name: shift lever
'
'            After sort by name:
'            ID: 1334   Name:
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'            ID: 1234   Name: crank arm
'            ID: 1434   Name: regular seat
'            ID: 1634   Name: shift lever

End Sub
End Class
``````

The following example demonstrates the Sort(Comparison<T>) method overload.

The example defines an alternative comparison method for strings, named `CompareDinosByLength`. This method works as follows: First, the comparands are tested for `null`, 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.

``````using namespace System;
using namespace System::Collections::Generic;

int CompareDinosByLength(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// 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 == nullptr)
// ...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);
}
}
}
};

void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
if (s == nullptr)
Console::WriteLine("(null)");
else
Console::WriteLine("\"{0}\"", s);
}
};

void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();
Display(dinosaurs);

Console::WriteLine("\nSort with generic Comparison<String^> delegate:");
dinosaurs->Sort(
gcnew Comparison<String^>(CompareDinosByLength));
Display(dinosaurs);

}

/* This code example produces the following output:

"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"

Sort with generic Comparison<String^> delegate:

(null)
""
"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 Main()
{
List<string> dinosaurs = new List<string>();
Display(dinosaurs);

Console.WriteLine("\nSort with generic Comparison<string> delegate:");
dinosaurs.Sort(CompareDinosByLength);
Display(dinosaurs);

}

private static void Display(List<string> list)
{
Console.WriteLine();
foreach( string s in list )
{
if (s == null)
Console.WriteLine("(null)");
else
Console.WriteLine("\"{0}\"", s);
}
}
}

/* This code example produces the following output:

"Pachycephalosaurus"
"Amargasaurus"
""
(null)
"Mamenchisaurus"
"Deinonychus"

Sort with generic Comparison<string> delegate:

(null)
""
"Deinonychus"
"Amargasaurus"
"Mamenchisaurus"
"Pachycephalosaurus"
*/
``````
``````Imports System
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 Main()

Dim dinosaurs As New List(Of String)
Display(dinosaurs)

Console.WriteLine(vbLf & "Sort with generic Comparison(Of String) delegate:")
Display(dinosaurs)

End Sub

Private Shared Sub Display(ByVal lis As List(Of String))
Console.WriteLine()
For Each s As String In lis
If s Is Nothing Then
Console.WriteLine("(Nothing)")
Else
Console.WriteLine("""{0}""", s)
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"
``````

Remarks

If `comparison` is provided, the elements of the List<T> are sorted using the method represented by the delegate.

If `comparison` is `null`, an ArgumentNullException is thrown.

This method uses Array.Sort, which applies the introspective sort as follows:

• If the partition size is fewer than 16 elements, it uses an insertion sort algorithm

• If the number of partitions exceeds 2 log n, 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.

On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n2) operation.

Sort(Int32, Int32, IComparer<T>)Sort(Int32, Int32, IComparer<T>)Sort(Int32, Int32, IComparer<T>)Sort(Int32, Int32, IComparer<T>)

Sorts the elements in a range of elements in List<T> using the specified comparer.

``````public:
void Sort(int index, int count, System::Collections::Generic::IComparer<T> ^ comparer);``````
``public void Sort (int index, int count, System.Collections.Generic.IComparer<T> comparer);``
``member this.Sort : int * int * System.Collections.Generic.IComparer<'T> -> unit``
``Public Sub Sort (index As Integer, count As Integer, comparer As IComparer(Of T))``

Parameters

index
Int32 Int32 Int32 Int32

The zero-based starting index of the range to sort.

count
Int32 Int32 Int32 Int32

The length of the range to sort.

comparer
IComparer<T> IComparer<T> IComparer<T> IComparer<T>

The IComparer<T> implementation to use when comparing elements, or `null` to use the default comparer Default.

Exceptions

`index` is less than 0.

-or-

`count` is less than 0.

`index` and `count` do not specify a valid range in the List<T>.

-or-

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 the default comparer Default cannot find implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

Examples

The following example demonstrates the Sort(Int32, Int32, IComparer<T>) method overload and the BinarySearch(Int32, Int32, T, IComparer<T>) method overload.

The example defines an alternative comparer for strings named DinoCompare, which implements the `IComparer<string>` (`IComparer(Of String)` in Visual Basic, `IComparer<String^>` in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for `null`, 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 the names of five herbivorous dinosaurs and three carnivorous dinosaurs. Within each of the two groups, the names are not in any particular sort order. The list is displayed, the range of herbivores is sorted using the alternate comparer, and the list is displayed again.

The BinarySearch(Int32, Int32, T, IComparer<T>) method overload is then used to search only the range of herbivores for "Brachiosaurus". The string is not found, and the bitwise complement (the ~ operator in C# and Visual C++, `Xor` -1 in Visual Basic) of the negative number returned by the BinarySearch(Int32, Int32, T, IComparer<T>) method is used as an index for inserting the new string.

``````using namespace System;
using namespace System::Collections::Generic;

public ref class DinoComparer: IComparer<String^>
{
public:
virtual int Compare(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// 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 == nullptr)
// ...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);
}
}
}
}
};

void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
Console::WriteLine(s);
}
};

void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();

int herbivores = 5;
Display(dinosaurs);

DinoComparer^ dc = gcnew DinoComparer();

Console::WriteLine("\nSort a range with the alternate comparer:");
dinosaurs->Sort(0, herbivores, dc);
Display(dinosaurs);

Console::WriteLine("\nBinarySearch a range and Insert \"{0}\":",
"Brachiosaurus");

int index = dinosaurs->BinarySearch(0, herbivores, "Brachiosaurus", dc);

if (index < 0)
{
dinosaurs->Insert(~index, "Brachiosaurus");
herbivores++;
}

Display(dinosaurs);
}

/* This code example produces the following output:

Pachycephalosaurus
Parasauralophus
Amargasaurus
Galimimus
Mamenchisaurus
Deinonychus
Oviraptor
Tyrannosaurus

Sort a range with the alternate comparer:

Galimimus
Amargasaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus

BinarySearch a range and Insert "Brachiosaurus":

Galimimus
Amargasaurus
Brachiosaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus
*/
``````
``````using System;
using System.Collections.Generic;

public class DinoComparer: IComparer<string>
{
public int Compare(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 class Example
{
public static void Main()
{
List<string> dinosaurs = new List<string>();

int herbivores = 5;
Display(dinosaurs);

DinoComparer dc = new DinoComparer();

Console.WriteLine("\nSort a range with the alternate comparer:");
dinosaurs.Sort(0, herbivores, dc);
Display(dinosaurs);

Console.WriteLine("\nBinarySearch a range and Insert \"{0}\":",
"Brachiosaurus");

int index = dinosaurs.BinarySearch(0, herbivores, "Brachiosaurus", dc);

if (index < 0)
{
dinosaurs.Insert(~index, "Brachiosaurus");
herbivores++;
}

Display(dinosaurs);
}

private static void Display(List<string> list)
{
Console.WriteLine();
foreach( string s in list )
{
Console.WriteLine(s);
}
}
}

/* This code example produces the following output:

Pachycephalosaurus
Parasauralophus
Amargasaurus
Galimimus
Mamenchisaurus
Deinonychus
Oviraptor
Tyrannosaurus

Sort a range with the alternate comparer:

Galimimus
Amargasaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus

BinarySearch a range and Insert "Brachiosaurus":

Galimimus
Amargasaurus
Brachiosaurus
Mamenchisaurus
Parasauralophus
Pachycephalosaurus
Deinonychus
Oviraptor
Tyrannosaurus
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class DinoComparer
Implements IComparer(Of String)

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

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
End Class

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)

Dim herbivores As Integer = 5
Display(dinosaurs)

Dim dc As New DinoComparer

Console.WriteLine(vbLf & _
"Sort a range with the alternate comparer:")
dinosaurs.Sort(0, herbivores, dc)
Display(dinosaurs)

Console.WriteLine(vbLf & _
"BinarySearch a range and Insert ""{0}"":", _
"Brachiosaurus")

Dim index As Integer = _
dinosaurs.BinarySearch(0, herbivores, "Brachiosaurus", dc)

If index < 0 Then
index = index Xor -1
dinosaurs.Insert(index, "Brachiosaurus")
herbivores += 1
End If

Display(dinosaurs)

End Sub

Private Shared Sub Display(ByVal lis As List(Of String))
Console.WriteLine()
For Each s As String In lis
Console.WriteLine(s)
Next
End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Parasauralophus
'Amargasaurus
'Galimimus
'Mamenchisaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
'
'Sort a range with the alternate comparer:
'
'Galimimus
'Amargasaurus
'Mamenchisaurus
'Parasauralophus
'Pachycephalosaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
'
'BinarySearch a range and Insert "Brachiosaurus":
'
'Galimimus
'Amargasaurus
'Brachiosaurus
'Mamenchisaurus
'Parasauralophus
'Pachycephalosaurus
'Deinonychus
'Oviraptor
'Tyrannosaurus
``````

Remarks

If `comparer` is provided, the elements of the List<T> are sorted using the specified IComparer<T> implementation.

If `comparer` is `null`, the default comparer Comparer<T>.Default checks whether type `T` implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type `T` implements the IComparable interface. If type `T` does not implement either interface, Comparer<T>.Default throws an InvalidOperationException.

This method uses Array.Sort, which applies the introspective sort as follows:

• If the partition size is fewer than 16 elements, it uses an insertion sort algorithm

• If the number of partitions exceeds 2 log n, 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.

On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n2) operation.

Sort()Sort()Sort()Sort()

Sorts the elements in the entire List<T> using the default comparer.

``````public:
void Sort();``````
``public void Sort ();``
``member this.Sort : unit -> unit``
``Public Sub Sort ()``

Exceptions

The default comparer Default cannot find an implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

Examples

The following example adds some names to a `List<String>` object, displays the list in unsorted order, calls the Sort method, and then displays the sorted list.

``````using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
String[] names = { "Samuel", "Dakota", "Koani", "Saya", "Vanya",
"Yiska", "Yuma", "Jody", "Nikita" };
var nameList = new List<String>();
Console.WriteLine("List in unsorted order: ");
foreach (var name in nameList)
Console.Write("   {0}", name);

Console.WriteLine(Environment.NewLine);

nameList.Sort();
Console.WriteLine("List in sorted order: ");
foreach (var name in nameList)
Console.Write("   {0}", name);

Console.WriteLine();
}
}
// The example displays the following output:
//    List in unsorted order:
//       Samuel   Dakota   Koani   Saya   Vanya   Yiska   Yuma   Jody   Nikita
//
//    List in sorted order:
//       Dakota   Jody   Koani   Nikita   Samuel   Saya   Vanya   Yiska   Yuma
``````
``````Imports System.Collections.Generic

Module Example
Public Sub Main()
Dim names() As String = { "Samuel", "Dakota", "Koani", "Saya",
"Vanya", "Yiska", "Yuma", "Jody",
"Nikita" }
Dim nameList As New List(Of String)()
Console.WriteLine("List in unsorted order: ")
For Each name In nameList
Console.Write("   {0}", name)
Next
Console.WriteLine(vbCrLf)

nameList.Sort()
Console.WriteLine("List in sorted order: ")
For Each name In nameList
Console.Write("   {0}", name)
Next
Console.WriteLine()
End Sub
End Module
' The example displays the following output:
'    List in unsorted order:
'       Samuel   Dakota   Koani   Saya   Vanya   Yiska   Yuma   Jody   Nikita
'
'    List in sorted order:
'       Dakota   Jody   Koani   Nikita   Samuel   Saya   Vanya   Yiska   Yuma
``````

The following code demonstrates the Sort() and Sort(Comparison<T>) method overloads on a simple business object. Calling the Sort() method results in the use of the default comparer for the Part type, and the Sort(Comparison<T>) method is implemented by using an anonymous method.

``````using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify the type of part
// but the part name can change.
public class Part : IEquatable<Part> , IComparable<Part>
{
public string PartName { get; set; }

public int PartId { get; set; }

public override string ToString()
{
return "ID: " + PartId + "   Name: " + PartName;
}
public override bool Equals(object obj)
{
if (obj == null) return false;
Part objAsPart = obj as Part;
if (objAsPart == null) return false;
else return Equals(objAsPart);
}
public int SortByNameAscending(string name1, string name2)
{

return name1.CompareTo(name2);
}

// Default comparer for Part type.
public int CompareTo(Part comparePart)
{
// A null value means that this object is greater.
if (comparePart == null)
return 1;

else
return this.PartId.CompareTo(comparePart.PartId);
}
public override int GetHashCode()
{
return PartId;
}
public bool Equals(Part other)
{
if (other == null) return false;
return (this.PartId.Equals(other.PartId));
}
// Should also override == and != operators.

}
public class Example
{
public static void Main()
{
// Create a list of parts.
List<Part> parts = new List<Part>();

// Add parts to the list.
parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
parts.Add(new Part() { PartName= "crank arm", PartId = 1234 });
parts.Add(new Part() { PartName = "shift lever", PartId = 1634 }); ;
// Name intentionally left null.
parts.Add(new Part() {  PartId = 1334 });
parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
parts.Add(new Part() { PartName = "cassette", PartId = 1534 });

// Write out the parts in the list. This will call the overridden
// ToString method in the Part class.
Console.WriteLine("\nBefore sort:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// Call Sort on the list. This will use the
// default comparer, which is the Compare method
// implemented on Part.
parts.Sort();

Console.WriteLine("\nAfter sort by part number:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

// This shows calling the Sort(Comparison(T) overload using
// an anonymous method for the Comparison delegate.
// This method treats null as the lesser of two values.
parts.Sort(delegate(Part x, Part y)
{
if (x.PartName == null && y.PartName == null) return 0;
else if (x.PartName == null) return -1;
else if (y.PartName == null) return 1;
else return x.PartName.CompareTo(y.PartName);
});

Console.WriteLine("\nAfter sort by name:");
foreach (Part aPart in parts)
{
Console.WriteLine(aPart);
}

/*

Before sort:
ID: 1434   Name: regular seat
ID: 1234   Name: crank arm
ID: 1634   Name: shift lever
ID: 1334   Name:
ID: 1444   Name: banana seat
ID: 1534   Name: cassette

After sort by part number:
ID: 1234   Name: crank arm
ID: 1334   Name:
ID: 1434   Name: regular seat
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1634   Name: shift lever

After sort by name:
ID: 1334   Name:
ID: 1444   Name: banana seat
ID: 1534   Name: cassette
ID: 1234   Name: crank arm
ID: 1434   Name: regular seat
ID: 1634   Name: shift lever

*/

}
}
``````
``````Imports System.Collections.Generic
' Simple business object. A PartId is used to identify the type of part
' but the part name can change.
Public Class Part
Implements IEquatable(Of Part)
Implements IComparable(Of Part)
Public Property PartName() As String
Get
Return m_PartName
End Get
Set(value As String)
m_PartName = Value
End Set
End Property
Private m_PartName As String

Public Property PartId() As Integer
Get
Return m_PartId
End Get
Set(value As Integer)
m_PartId = Value
End Set
End Property
Private m_PartId As Integer

Public Overrides Function ToString() As String
Return "ID: " & PartId & "   Name: " & PartName
End Function

Public Overrides Function Equals(obj As Object) As Boolean
If obj Is Nothing Then
Return False
End If
Dim objAsPart As Part = TryCast(obj, Part)
If objAsPart Is Nothing Then
Return False
Else
Return Equals(objAsPart)
End If
End Function

Public Function SortByNameAscending(name1 As String, name2 As String) As Integer

Return name1.CompareTo(name2)
End Function

' Default comparer for Part.
Public Function CompareTo(comparePart As Part) As Integer _
Implements IComparable(Of ListSortVB.Part).CompareTo
' A null value means that this object is greater.
If comparePart Is Nothing Then
Return 1
Else

Return Me.PartId.CompareTo(comparePart.PartId)
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return PartId
End Function
Public Overloads Function Equals(other As Part) As Boolean Implements IEquatable(Of ListSortVB.Part).Equals
If other Is Nothing Then
Return False
End If
Return (Me.PartId.Equals(other.PartId))
End Function
' Should also override == and != operators.

End Class
Public Class Example
Public Shared Sub Main()
' Create a list of parts.
Dim parts As New List(Of Part)()

' Add parts to the list.
.PartName = "regular seat", _
.PartId = 1434 _
})
.PartName = "crank arm", _
.PartId = 1234 _
})
.PartName = "shift lever", _
.PartId = 1634 _
})

' Name intentionally left null.
.PartId = 1334 _
})
.PartName = "banana seat", _
.PartId = 1444 _
})
.PartName = "cassette", _
.PartId = 1534 _
})

' Write out the parts in the list. This will call the overridden
' ToString method in the Part class.
Console.WriteLine(vbLf & "Before sort:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' Call Sort on the list. This will use the
' default comparer, which is the Compare method
' implemented on Part.
parts.Sort()

Console.WriteLine(vbLf & "After sort by part number:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

' This shows calling the Sort(Comparison(T) overload using
' an anonymous delegate method.
' This method treats null as the lesser of two values.
parts.Sort(Function(x As Part, y As Part)
If x.PartName Is Nothing AndAlso y.PartName Is Nothing Then
Return 0
ElseIf x.PartName Is Nothing Then
Return -1
ElseIf y.PartName Is Nothing Then
Return 1
Else
Return x.PartName.CompareTo(y.PartName)
End If
End Function)

Console.WriteLine(vbLf & "After sort by name:")
For Each aPart As Part In parts
Console.WriteLine(aPart)
Next

'
'
'            Before sort:
'            ID: 1434   Name: regular seat
'            ID: 1234   Name: crank arm
'            ID: 1634   Name: shift lever
'            ID: 1334   Name:
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'
'            After sort by part number:
'            ID: 1234   Name: crank arm
'            ID: 1334   Name:
'            ID: 1434   Name: regular seat
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'            ID: 1634   Name: shift lever
'
'            After sort by name:
'            ID: 1334   Name:
'            ID: 1444   Name: banana seat
'            ID: 1534   Name: cassette
'            ID: 1234   Name: crank arm
'            ID: 1434   Name: regular seat
'            ID: 1634   Name: shift lever

End Sub
End Class
``````

The following example demonstrates the Sort() method overload and the BinarySearch(T) method overload. A List<T> of strings is created and populated with four strings, in no particular order. The list is displayed, sorted, and displayed again.

The BinarySearch(T) method overload is then used to search for two strings that are not in the list, and the Insert method is used to insert them. The return value of the BinarySearch method is negative in each case, because the strings are not in the list. Taking the bitwise complement (the ~ operator in C# and Visual C++, `Xor` -1 in Visual Basic) of this negative number produces the index of the first element in the list that is larger than the search string, and inserting at this location preserves the sort order. The second search string is larger than any element in the list, so the insertion position is at the end of the list.

``````using namespace System;
using namespace System::Collections::Generic;

void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();

Console::WriteLine();
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}

Console::WriteLine("\nSort");
dinosaurs->Sort();

Console::WriteLine();
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}

Console::WriteLine("\nBinarySearch and Insert \"Coelophysis\":");
int index = dinosaurs->BinarySearch("Coelophysis");
if (index < 0)
{
dinosaurs->Insert(~index, "Coelophysis");
}

Console::WriteLine();
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}

Console::WriteLine("\nBinarySearch and Insert \"Tyrannosaurus\":");
index = dinosaurs->BinarySearch("Tyrannosaurus");
if (index < 0)
{
dinosaurs->Insert(~index, "Tyrannosaurus");
}

Console::WriteLine();
for each(String^ dinosaur in dinosaurs)
{
Console::WriteLine(dinosaur);
}
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort

Amargasaurus
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaurus":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus
Tyrannosaurus
*/
``````
``````using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
List<string> dinosaurs = new List<string>();

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine("\nSort");
dinosaurs.Sort();

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine("\nBinarySearch and Insert \"Coelophysis\":");
int index = dinosaurs.BinarySearch("Coelophysis");
if (index < 0)
{
dinosaurs.Insert(~index, "Coelophysis");
}

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}

Console.WriteLine("\nBinarySearch and Insert \"Tyrannosaurus\":");
index = dinosaurs.BinarySearch("Tyrannosaurus");
if (index < 0)
{
dinosaurs.Insert(~index, "Tyrannosaurus");
}

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
Console.WriteLine(dinosaur);
}
}
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort

Amargasaurus
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaurus":

Amargasaurus
Coelophysis
Deinonychus
Mamenchisaurus
Pachycephalosaurus
Tyrannosaurus
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)

Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & "Sort")
dinosaurs.Sort

Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & _
"BinarySearch and Insert ""Coelophysis"":")
Dim index As Integer = dinosaurs.BinarySearch("Coelophysis")
If index < 0 Then
index = index Xor -1
dinosaurs.Insert(index, "Coelophysis")
End If

Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

Console.WriteLine(vbLf & _
"BinarySearch and Insert ""Tyrannosaurus"":")
index = dinosaurs.BinarySearch("Tyrannosaurus")
If index < 0 Then
index = index Xor -1
dinosaurs.Insert(index, "Tyrannosaurus")
End If

Console.WriteLine()
For Each dinosaur As String In dinosaurs
Console.WriteLine(dinosaur)
Next

End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'Sort
'
'Amargasaurus
'Deinonychus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Coelophysis":
'
'Amargasaurus
'Coelophysis
'Deinonychus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Tyrannosaurus":
'
'Amargasaurus
'Coelophysis
'Deinonychus
'Mamenchisaurus
'Pachycephalosaurus
'Tyrannosaurus
``````

Remarks

This method uses the default comparer Comparer<T>.Default for type `T` to determine the order of list elements. The Comparer<T>.Default property checks whether type `T` implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type `T` implements the IComparable interface. If type `T` does not implement either interface, Comparer<T>.Default throws an InvalidOperationException.

This method uses the Array.Sort method, which applies the introspective sort as follows:

• If the partition size is fewer than 16 elements, it uses an insertion sort algorithm.

• If the number of partitions exceeds 2 log n, 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.

On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n2) operation.

Sort(IComparer<T>)Sort(IComparer<T>)Sort(IComparer<T>)Sort(IComparer<T>)

Sorts the elements in the entire List<T> using the specified comparer.

``````public:
void Sort(System::Collections::Generic::IComparer<T> ^ comparer);``````
``public void Sort (System.Collections.Generic.IComparer<T> comparer);``
``member this.Sort : System.Collections.Generic.IComparer<'T> -> unit``
``Public Sub Sort (comparer As IComparer(Of T))``

Parameters

comparer
IComparer<T> IComparer<T> IComparer<T> IComparer<T>

The IComparer<T> implementation to use when comparing elements, or `null` to use the default comparer Default.

Exceptions

`comparer` is `null`, and the default comparer Default cannot find implementation of the IComparable<T> generic interface or the IComparable interface for type `T`.

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

Examples

The following example demonstrates the Sort(IComparer<T>) method overload and the BinarySearch(T, IComparer<T>) method overload.

The example defines an alternative comparer for strings named DinoCompare, which implements the `IComparer<string>` (`IComparer(Of String)` in Visual Basic, `IComparer<String^>` in Visual C++) generic interface. The comparer works as follows: First, the comparands are tested for `null`, 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 is displayed, sorted using the alternate comparer, and displayed again.

The BinarySearch(T, IComparer<T>) method overload is then used to search for several strings that are not in the list, employing the alternate comparer. The Insert method is used to insert the strings. These two methods are located in the function named `SearchAndInsert`, along with code to take the bitwise complement (the ~ operator in C# and Visual C++, `Xor` -1 in Visual Basic) of the negative number returned by BinarySearch(T, IComparer<T>) and use it as an index for inserting the new string.

``````using namespace System;
using namespace System::Collections::Generic;

public ref class DinoComparer: IComparer<String^>
{
public:
virtual int Compare(String^ x, String^ y)
{
if (x == nullptr)
{
if (y == nullptr)
{
// 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 == nullptr)
// ...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);
}
}
}
}
};

void SearchAndInsert(List<String^>^ list, String^ insert,
DinoComparer^ dc)
{
Console::WriteLine("\nBinarySearch and Insert \"{0}\":", insert);

int index = list->BinarySearch(insert, dc);

if (index < 0)
{
list->Insert(~index, insert);
}
};

void Display(List<String^>^ list)
{
Console::WriteLine();
for each(String^ s in list)
{
Console::WriteLine(s);
}
};

void main()
{
List<String^>^ dinosaurs = gcnew List<String^>();
Display(dinosaurs);

DinoComparer^ dc = gcnew DinoComparer();

Console::WriteLine("\nSort with alternate comparer:");
dinosaurs->Sort(dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Coelophysis", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Oviraptor", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Tyrannosaur", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, nullptr, dc);
Display(dinosaurs);
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort with alternate comparer:

Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Oviraptor":

Oviraptor
Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaur":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus
*/
``````
``````using System;
using System.Collections.Generic;

public class DinoComparer: IComparer<string>
{
public int Compare(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 class Example
{
public static void Main()
{
List<string> dinosaurs = new List<string>();
Display(dinosaurs);

DinoComparer dc = new DinoComparer();

Console.WriteLine("\nSort with alternate comparer:");
dinosaurs.Sort(dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Coelophysis", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Oviraptor", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, "Tyrannosaur", dc);
Display(dinosaurs);

SearchAndInsert(dinosaurs, null, dc);
Display(dinosaurs);
}

private static void SearchAndInsert(List<string> list,
string insert, DinoComparer dc)
{
Console.WriteLine("\nBinarySearch and Insert \"{0}\":", insert);

int index = list.BinarySearch(insert, dc);

if (index < 0)
{
list.Insert(~index, insert);
}
}

private static void Display(List<string> list)
{
Console.WriteLine();
foreach( string s in list )
{
Console.WriteLine(s);
}
}
}

/* This code example produces the following output:

Pachycephalosaurus
Amargasaurus
Mamenchisaurus
Deinonychus

Sort with alternate comparer:

Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Coelophysis":

Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Oviraptor":

Oviraptor
Coelophysis
Deinonychus
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "Tyrannosaur":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus

BinarySearch and Insert "":

Oviraptor
Coelophysis
Deinonychus
Tyrannosaur
Amargasaurus
Mamenchisaurus
Pachycephalosaurus
*/
``````
``````Imports System
Imports System.Collections.Generic

Public Class DinoComparer
Implements IComparer(Of String)

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

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
End Class

Public Class Example

Public Shared Sub Main()

Dim dinosaurs As New List(Of String)
Display(dinosaurs)

Dim dc As New DinoComparer

Console.WriteLine(vbLf & "Sort with alternate comparer:")
dinosaurs.Sort(dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Coelophysis", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Oviraptor", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, "Tyrannosaur", dc)
Display(dinosaurs)

SearchAndInsert(dinosaurs, Nothing, dc)
Display(dinosaurs)
End Sub

Private Shared Sub SearchAndInsert( _
ByVal lis As List(Of String), _
ByVal insert As String, ByVal dc As DinoComparer)

Console.WriteLine(vbLf & _
"BinarySearch and Insert ""{0}"":", insert)

Dim index As Integer = lis.BinarySearch(insert, dc)

If index < 0 Then
index = index Xor -1
lis.Insert(index, insert)
End If
End Sub

Private Shared Sub Display(ByVal lis As List(Of String))
Console.WriteLine()
For Each s As String In lis
Console.WriteLine(s)
Next
End Sub
End Class

' This code example produces the following output:
'
'Pachycephalosaurus
'Amargasaurus
'Mamenchisaurus
'Deinonychus
'
'Sort with alternate comparer:
'
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Coelophysis":
'
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Oviraptor":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "Tyrannosaur":
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
'
'BinarySearch and Insert "":
'
'
'Oviraptor
'Coelophysis
'Deinonychus
'Tyrannosaur
'Amargasaurus
'Mamenchisaurus
'Pachycephalosaurus
``````

Remarks

If `comparer` is provided, the elements of the List<T> are sorted using the specified IComparer<T> implementation.

If `comparer` is `null`, the default comparer Comparer<T>.Default checks whether type `T` implements the IComparable<T> generic interface and uses that implementation, if available. If not, Comparer<T>.Default checks whether type `T` implements the IComparable interface. If type `T` does not implement either interface, Comparer<T>.Default throws an InvalidOperationException.

This method uses the Array.Sort method, which applies the introspective sort as follows:

• If the partition size is fewer than 16 elements, it uses an insertion sort algorithm.

• If the number of partitions exceeds 2 log n, 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.

On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n2) operation.