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Array.FindIndex(Of T) Method (T(), Predicate(Of T))

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

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

'Declaration
Public Shared Function FindIndex(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
Type: T()

The one-dimensional, zero-based Array 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 first occurrence of an element that matches the conditions defined by match, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

array is Nothing.

-or-

match is Nothing.

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

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 the Length of array.

The following code example demonstrates all three overloads of the FindIndex 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 FindIndex(Of T)(T(), Predicate(Of T)) method overload traverses the array from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element at position 1.

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 FindIndex(Of T)(T(), Int32, Predicate(Of T)) method overload is used to search the array beginning at position 2 and continuing to the end of the array. It finds the element at position 5. Finally, the FindIndex(Of T)(T(), Int32, Int32, Predicate(Of T)) method overload is used to search the range of three elements beginning at position 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.FindIndex(dinosaurs, AddressOf EndsWithSaurus): {0}", _
            Array.FindIndex(dinosaurs, AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus): {0}", _
            Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Array.FindIndex(dinosaurs, 2, 3, AddressOf EndsWithSaurus): {0}", _
            Array.FindIndex(dinosaurs, 2, 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.FindIndex(dinosaurs, AddressOf EndsWithSaurus): 1 

'Array.FindIndex(dinosaurs, 2, AddressOf EndsWithSaurus): 5 

'Array.FindIndex(dinosaurs, 2, 3, AddressOf EndsWithSaurus): -1

.NET Framework

Supported in: 4.6, 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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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