Array.FindLastIndex(Of T) Method (T(), Int32, Int32, Predicate(Of 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.

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

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


Type: T()

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

Type: System.Int32

The zero-based starting index of the backward search.

Type: System.Int32

The number of elements in the section to search.

Type: System.Predicate(Of T)

The Predicate(Of 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


The type of the elements of the array.

Exception Condition

array is null.


match is null.


startIndex is outside the range of valid indexes for array.


count is less than zero.


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

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

The Predicate(Of 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(Of T).

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

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(Of T)(T(), Predicate(Of 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.


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(Of T)(T(), Int32, Predicate(Of 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(Of T)(T(), Int32, Int32, Predicate(Of 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".

Imports System

Public Class Example

    Public Shared Sub Main()

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

        For Each dinosaur As String In dinosaurs

        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
            Return False
        End If
    End Function
End Class

' This code example produces the following output:
'Array.FindLastIndex(dinosaurs, AddressOf EndsWithSaurus): 5
'Array.FindLastIndex(dinosaurs, 4, AddressOf EndsWithSaurus): 1
'Array.FindLastIndex(dinosaurs, 4, 3, AddressOf 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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