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)

'Declaration
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
Type: T()

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

startIndex
Type: System.Int32

The zero-based starting index of the backward search.

count
Type: System.Int32

The number of elements in the section to search.

match
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.

ExceptionCondition
ArgumentNullException

array is Nothing.

-or-

match is Nothing.

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.

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.

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(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" }

        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

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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