Array.FindLastIndex Method

Definition

Namespace:

System

Assemblies:

netstandard.dll, 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".

C#

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
 */

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.

C#

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

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.

C#

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

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.

C#

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

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>