FindLastIndex(T) Method (T[], Predicate(T))
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Array.FindLastIndex<T> Method (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.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

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

Parameters

array
Type: T[]

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

match
Type: System.Predicate<T>

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

Return Value

Type: System.Int32

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

Type Parameters

T

The type of the elements of the array.

Exception Condition
ArgumentNullException

array is null.

-or-

match is null.

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.

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.

System_CAPS_noteNote

In C# 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 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
 */

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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