Array.FindLastIndex Method

Definition

Namespace:

System

Assembly:

System.Runtime.dll

Searches for an element that matches the conditions defined by a specified predicate, and returns the zero-based index of the last occurrence within an Array or a portion of it.

Overloads

FindLastIndex<T>(T[], Predicate<T>)	Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the entire Array.
FindLastIndex<T>(T[], Int32, Predicate<T>)	Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the Array that extends from the first element to the specified index.
FindLastIndex<T>(T[], Int32, Int32, Predicate<T>)	Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the Array that contains the specified number of elements and ends at the specified index.

Examples

The following code example demonstrates all three overloads of the FindLastIndex generic method. An array of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The code example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".

The FindLastIndex<T>(T[], Predicate<T>) method overload traverses the array backward from the end, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element at position 5.

Note

In C#, F# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context and create it automatically.

The FindLastIndex<T>(T[], Int32, Predicate<T>) method overload is used to search the array beginning at position 4 and continuing backward to the beginning of the array. It finds the element at position 1. Finally, the FindLastIndex<T>(T[], Int32, Int32, Predicate<T>) method overload is used to search the range of three elements beginning at position 4 and working backward (that is, elements 4, 3, and 2). It returns -1 because there are no dinosaur names in that range that end with "saurus".

using namespace System;

// Search predicate returns true if a string ends in "saurus".
bool EndsWithSaurus(String^ s)
{
    if ((s->Length > 5) && 
        (s->Substring(s->Length - 6)->ToLower() == "saurus"))
    {
        return true;
    }
    else
    {
        return false;
    }
};

void main()
{
    array<String^>^ dinosaurs = { "Compsognathus", 
        "Amargasaurus",   "Oviraptor",      "Velociraptor", 
        "Deinonychus",    "Dilophosaurus",  "Gallimimus", 
        "Triceratops" };

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

    Console::WriteLine("\nArray::FindLastIndex(dinosaurs, EndsWithSaurus): {0}", 
        Array::FindLastIndex(dinosaurs, gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nArray::FindLastIndex(dinosaurs, 4, EndsWithSaurus): {0}",
        Array::FindLastIndex(dinosaurs, 4, gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nArray::FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): {0}",
        Array::FindLastIndex(dinosaurs, 4, 3, gcnew Predicate<String^>(EndsWithSaurus)));
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

Array::FindLastIndex(dinosaurs, EndsWithSaurus): 5

Array::FindLastIndex(dinosaurs, 4, EndsWithSaurus): 1

Array::FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): -1
 */

using System;

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = { "Compsognathus",
            "Amargasaurus",   "Oviraptor",      "Velociraptor",
            "Deinonychus",    "Dilophosaurus",  "Gallimimus",
            "Triceratops" };

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

        Console.WriteLine(
            "\nArray.FindLastIndex(dinosaurs, EndsWithSaurus): {0}",
            Array.FindLastIndex(dinosaurs, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindLastIndex(dinosaurs, 4, EndsWithSaurus): {0}",
            Array.FindLastIndex(dinosaurs, 4, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): {0}",
            Array.FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus));
    }

    // Search predicate returns true if a string ends in "saurus".
    private static bool EndsWithSaurus(String s)
    {
        if ((s.Length > 5) &&
            (s.Substring(s.Length - 6).ToLower() == "saurus"))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

Array.FindLastIndex(dinosaurs, EndsWithSaurus): 5

Array.FindLastIndex(dinosaurs, 4, EndsWithSaurus): 1

Array.FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): -1
 */

open System

// Search predicate returns true if a string ends in "saurus".
let endsWithSaurus (s: string) =
    s.Length > 5 && s.Substring(s.Length - 6).ToLower() = "saurus"

let dinosaurs =
    [| "Compsognathus"; "Amargasaurus"
       "Oviraptor"; "Velociraptor"
       "Deinonychus"; "Dilophosaurus"
       "Gallimimus"; "Triceratops" |]

printfn ""
for dino in dinosaurs do
    printfn $"{dino}"

Array.FindLastIndex(dinosaurs, endsWithSaurus)
|> printfn "\nArray.FindLastIndex(dinosaurs, EndsWithSaurus): %i"

Array.FindLastIndex(dinosaurs, 4, endsWithSaurus)
|> printfn "\nArray.FindLastIndex(dinosaurs, 4, EndsWithSaurus): %i"

Array.FindLastIndex(dinosaurs, 4, 3, endsWithSaurus)
|> printfn "\nArray.FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): %i"


// This code example produces the following output:
//
//     Compsognathus
//     Amargasaurus
//     Oviraptor
//     Velociraptor
//     Deinonychus
//     Dilophosaurus
//     Gallimimus
//     Triceratops
//
//     Array.FindLastIndex(dinosaurs, EndsWithSaurus): 5
//
//     Array.FindLastIndex(dinosaurs, 4, EndsWithSaurus): 1
//
//     Array.FindLastIndex(dinosaurs, 4, 3, EndsWithSaurus): -1

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs() As String = { "Compsognathus", _
            "Amargasaurus",   "Oviraptor",      "Velociraptor", _
            "Deinonychus",    "Dilophosaurus",  "Gallimimus", _
            "Triceratops" }

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

        Console.WriteLine(vbLf & _
            "Array.FindLastIndex(dinosaurs, AddressOf EndsWithSaurus): {0}", _
            Array.FindLastIndex(dinosaurs, AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Array.FindLastIndex(dinosaurs, 4, AddressOf EndsWithSaurus): {0}", _
            Array.FindLastIndex(dinosaurs, 4, AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Array.FindLastIndex(dinosaurs, 4, 3, AddressOf EndsWithSaurus): {0}", _
            Array.FindLastIndex(dinosaurs, 4, 3, AddressOf EndsWithSaurus))

    End Sub

    ' Search predicate returns true if a string ends in "saurus".
    Private Shared Function EndsWithSaurus(ByVal s As String) _
        As Boolean

        ' AndAlso prevents evaluation of the second Boolean
        ' expression if the string is so short that an error
        ' would occur.
        If (s.Length > 5) AndAlso _
            (s.Substring(s.Length - 6).ToLower() = "saurus") Then
            Return True
        Else
            Return False
        End If
    End Function
End Class

' This code example produces the following output:
'
'Compsognathus
'Amargasaurus
'Oviraptor
'Velociraptor
'Deinonychus
'Dilophosaurus
'Gallimimus
'Triceratops
'
'Array.FindLastIndex(dinosaurs, AddressOf EndsWithSaurus): 5
'
'Array.FindLastIndex(dinosaurs, 4, AddressOf EndsWithSaurus): 1
'
'Array.FindLastIndex(dinosaurs, 4, 3, AddressOf EndsWithSaurus): -1

FindLastIndex<T>(T[], Predicate<T>)

Source:

Array.cs

Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the entire Array.

public:
generic <typename T>
 static int FindLastIndex(cli::array <T> ^ array, Predicate<T> ^ match);

public static int FindLastIndex<T> (T[] array, Predicate<T> match);

static member FindLastIndex : 'T[] * Predicate<'T> -> int

Public Shared Function FindLastIndex(Of T) (array As T(), match As Predicate(Of T)) As Integer

Type Parameters

T

The type of the elements of the array.

Parameters

array

T[]

The one-dimensional, zero-based Array to search.

match

Predicate<T>

The Predicate<T> that defines the conditions of the element to search for.

Returns

Int32

The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Exceptions

ArgumentNullException

array is null.

-or-

match is null.

Remarks

The Array is searched backward starting at the last element and ending at the first element.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate<T>.

This method is an O(n) operation, where n is the Length of array.

See also

• Exists<T>(T[], Predicate<T>)
• Find<T>(T[], Predicate<T>)
• FindLast<T>(T[], Predicate<T>)
• FindAll<T>(T[], Predicate<T>)
• BinarySearch
• IndexOf
• LastIndexOf
• Predicate<T>

FindLastIndex<T>(T[], Int32, Predicate<T>)

Source:

Array.cs

Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the Array that extends from the first element to the specified index.

public:
generic <typename T>
 static int FindLastIndex(cli::array <T> ^ array, int startIndex, Predicate<T> ^ match);

public static int FindLastIndex<T> (T[] array, int startIndex, Predicate<T> match);

static member FindLastIndex : 'T[] * int * Predicate<'T> -> int

Public Shared Function FindLastIndex(Of T) (array As T(), startIndex As Integer, match As Predicate(Of T)) As Integer

Type Parameters

T

The type of the elements of the array.

Parameters

array

T[]

The one-dimensional, zero-based Array to search.

startIndex

Int32

The zero-based starting index of the backward search.

match

Predicate<T>

The Predicate<T> that defines the conditions of the element to search for.

Returns

Int32

The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Exceptions

ArgumentNullException

array is null.

-or-

match is null.

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for array.

Remarks

The Array is searched backward starting at startIndex and ending at the first element.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate<T>.

This method is an O(n) operation, where n is the number of elements from the beginning of array to startIndex.

See also

• Exists<T>(T[], Predicate<T>)
• Find<T>(T[], Predicate<T>)
• FindLast<T>(T[], Predicate<T>)
• FindAll<T>(T[], Predicate<T>)
• BinarySearch
• IndexOf
• LastIndexOf
• Predicate<T>

FindLastIndex<T>(T[], Int32, Int32, Predicate<T>)

Source:

Array.cs

Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the last occurrence within the range of elements in the Array that contains the specified number of elements and ends at the specified index.

public:
generic <typename T>
 static int FindLastIndex(cli::array <T> ^ array, int startIndex, int count, Predicate<T> ^ match);

public static int FindLastIndex<T> (T[] array, int startIndex, int count, Predicate<T> match);

static member FindLastIndex : 'T[] * int * int * Predicate<'T> -> int

Public Shared Function FindLastIndex(Of T) (array As T(), startIndex As Integer, count As Integer, match As Predicate(Of T)) As Integer

Type Parameters

T

The type of the elements of the array.

Parameters

array

T[]

The one-dimensional, zero-based Array to search.

startIndex

Int32

The zero-based starting index of the backward search.

count

Int32

The number of elements in the section to search.

match

Predicate<T>

The Predicate<T> that defines the conditions of the element to search for.

Returns

Int32

The zero-based index of the last occurrence of an element that matches the conditions defined by match, if found; otherwise, -1.

Exceptions

ArgumentNullException

array is null.

-or-

match is null.

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for array.

-or-

count is less than zero.

-or-

startIndex and count do not specify a valid section in array.

Remarks

The Array is searched backward starting at startIndex and ending at startIndex minus count plus 1, if count is greater than 0.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate<T>.

This method is an O(n) operation, where n is count.

See also

• Exists<T>(T[], Predicate<T>)
• Find<T>(T[], Predicate<T>)
• FindLast<T>(T[], Predicate<T>)
• FindAll<T>(T[], Predicate<T>)
• BinarySearch
• IndexOf
• LastIndexOf
• Predicate<T>