List<T>.LastIndexOf Method

Definition

Namespace:

System.Collections.Generic

Assembly:

System.Collections.dll

Returns the zero-based index of the last occurrence of a value in the List<T> or in a portion of it.

Overloads

LastIndexOf(T)	Searches for the specified object and returns the zero-based index of the last occurrence within the entire List<T>.
LastIndexOf(T, Int32)	Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that extends from the first element to the specified index.
LastIndexOf(T, Int32, Int32)	Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that contains the specified number of elements and ends at the specified index.

Examples

The following example demonstrates all three overloads of the LastIndexOf method. A List<T> of strings is created, with one entry that appears twice, at index location 0 and index location 5. The LastIndexOf(T) method overload searches the entire list from the end, and finds the second occurrence of the string. The LastIndexOf(T, Int32) method overload is used to search the list backward beginning with index location 3 and continuing to the beginning of the list, so it finds the first occurrence of the string in the list. Finally, the LastIndexOf(T, Int32, Int32) method overload is used to search a range of four entries, beginning at index location 4 and extending backward (that is, it searches the items at locations 4, 3, 2, and 1); this search returns -1 because there are no instances of the search string in that range.

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

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

    dinosaurs->Add("Tyrannosaurus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Mamenchisaurus");
    dinosaurs->Add("Brachiosaurus");
    dinosaurs->Add("Deinonychus");
    dinosaurs->Add("Tyrannosaurus");
    dinosaurs->Add("Compsognathus");

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

    Console::WriteLine("\nLastIndexOf(\"Tyrannosaurus\"): {0}", 
        dinosaurs->LastIndexOf("Tyrannosaurus"));

    Console::WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 3): {0}", 
        dinosaurs->LastIndexOf("Tyrannosaurus", 3));

    Console::WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 4, 4): {0}", 
        dinosaurs->LastIndexOf("Tyrannosaurus", 4, 4));
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

LastIndexOf("Tyrannosaurus"): 5

LastIndexOf("Tyrannosaurus", 3): 0

LastIndexOf("Tyrannosaurus", 4, 4): -1
 */

using System;
using System.Collections.Generic;

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

        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Mamenchisaurus");
        dinosaurs.Add("Brachiosaurus");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Tyrannosaurus");
        dinosaurs.Add("Compsognathus");

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

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\"): {0}",
            dinosaurs.LastIndexOf("Tyrannosaurus"));

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 3): {0}",
            dinosaurs.LastIndexOf("Tyrannosaurus", 3));

        Console.WriteLine("\nLastIndexOf(\"Tyrannosaurus\", 4, 4): {0}",
            dinosaurs.LastIndexOf("Tyrannosaurus", 4, 4));
    }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

LastIndexOf("Tyrannosaurus"): 5

LastIndexOf("Tyrannosaurus", 3): 0

LastIndexOf("Tyrannosaurus", 4, 4): -1
 */

Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Mamenchisaurus")
        dinosaurs.Add("Brachiosaurus")
        dinosaurs.Add("Deinonychus")
        dinosaurs.Add("Tyrannosaurus")
        dinosaurs.Add("Compsognathus")

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

        Console.WriteLine(vbLf & _
            "LastIndexOf(""Tyrannosaurus""): {0}", _
            dinosaurs.LastIndexOf("Tyrannosaurus"))

        Console.WriteLine(vbLf & _
            "LastIndexOf(""Tyrannosaurus"", 3): {0}", _
            dinosaurs.LastIndexOf("Tyrannosaurus", 3))

        Console.WriteLine(vbLf & _
            "LastIndexOf(""Tyrannosaurus"", 4, 4): {0}", _
            dinosaurs.LastIndexOf("Tyrannosaurus", 4, 4))

    End Sub
End Class

' This code example produces the following output:
'
'Tyrannosaurus
'Amargasaurus
'Mamenchisaurus
'Brachiosaurus
'Deinonychus
'Tyrannosaurus
'Compsognathus
'
'LastIndexOf("Tyrannosaurus"): 5
'
'LastIndexOf("Tyrannosaurus", 3): 0
'
'LastIndexOf("Tyrannosaurus", 4, 4): -1

LastIndexOf(T)

Source:

List.cs

Searches for the specified object and returns the zero-based index of the last occurrence within the entire List<T>.

public:
 int LastIndexOf(T item);

public int LastIndexOf (T item);

member this.LastIndexOf : 'T -> int

Public Function LastIndexOf (item As T) As Integer

Parameters

item

T

The object to locate in the List<T>. The value can be null for reference types.

Returns

Int32

The zero-based index of the last occurrence of item within the entire the List<T>, if found; otherwise, -1.

Remarks

The List<T> is searched backward starting at the last element and ending at the first element.

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

See also

• IndexOf(T)
• Contains(T)
• Performing Culture-Insensitive String Operations in Collections

LastIndexOf(T, Int32)

Source:

List.cs

Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that extends from the first element to the specified index.

public:
 int LastIndexOf(T item, int index);

public int LastIndexOf (T item, int index);

member this.LastIndexOf : 'T * int -> int

Public Function LastIndexOf (item As T, index As Integer) As Integer

Parameters

item

T

The object to locate in the List<T>. The value can be null for reference types.

index

Int32

The zero-based starting index of the backward search.

Returns

Int32

The zero-based index of the last occurrence of item within the range of elements in the List<T> that extends from the first element to index, if found; otherwise, -1.

Exceptions

ArgumentOutOfRangeException

index is outside the range of valid indexes for the List<T>.

Remarks

The List<T> is searched backward starting at index and ending at the first element.

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

This method performs a linear search; therefore, this method is an O(n) operation, where n is the number of elements from the beginning of the List<T> to index.

See also

• IndexOf(T)
• Contains(T)
• Performing Culture-Insensitive String Operations in Collections

LastIndexOf(T, Int32, Int32)

Source:

List.cs

Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that contains the specified number of elements and ends at the specified index.

public:
 int LastIndexOf(T item, int index, int count);

public int LastIndexOf (T item, int index, int count);

member this.LastIndexOf : 'T * int * int -> int

Public Function LastIndexOf (item As T, index As Integer, count As Integer) As Integer

Parameters

item

T

The object to locate in the List<T>. The value can be null for reference types.

index

Int32

The zero-based starting index of the backward search.

count

Int32

The number of elements in the section to search.

Returns

Int32

The zero-based index of the last occurrence of item within the range of elements in the List<T> that contains count number of elements and ends at index, if found; otherwise, -1.

Exceptions

ArgumentOutOfRangeException

index is outside the range of valid indexes for the List<T>.

-or-

count is less than 0.

-or-

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

Remarks

The List<T> is searched backward starting at index and ending at index minus count plus 1, if count is greater than 0.

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

This method performs a linear search; therefore, this method is an O(n) operation, where n is count.

See also

• IndexOf(T)
• Contains(T)
• Performing Culture-Insensitive String Operations in Collections