Array.FindIndex Method

Definition

Namespace:

System

Assembly:

System.Runtime.dll

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

Overloads

FindIndex<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 first occurrence within the entire Array.
FindIndex<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 first occurrence within the range of elements in the Array that extends from the specified index to the last element.
FindIndex<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 first occurrence within the range of elements in the Array that starts at the specified index and contains the specified number of elements.

Examples

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<T>(T[], Predicate<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.

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 FindIndex<T>(T[], Int32, Predicate<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<T>(T[], Int32, Int32, Predicate<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".

using namespace System;

// Search predicate returns true if a string ends in "saurus".
bool EndsWithSaurus(String^ s)
{
    if ((s->Length > 5) && 
        (s->Substring(s->Length - 6)->ToLower() == "saurus"))
    {
        return true;
    }
    else
    {
        return false;
    }
};

void main()
{
    array<String^>^ dinosaurs = { "Compsognathus", 
        "Amargasaurus",   "Oviraptor",      "Velociraptor", 
        "Deinonychus",    "Dilophosaurus",  "Gallimimus", 
        "Triceratops" };

    Console::WriteLine();
    for each(String^ dinosaur in dinosaurs )
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nArray::FindIndex(dinosaurs, EndsWithSaurus): {0}", 
        Array::FindIndex(dinosaurs, gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nArray::FindIndex(dinosaurs, 2, EndsWithSaurus): {0}",
        Array::FindIndex(dinosaurs, 2, gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nArray::FindIndex(dinosaurs, 2, 3, EndsWithSaurus): {0}",
        Array::FindIndex(dinosaurs, 2, 3, gcnew Predicate<String^>(EndsWithSaurus)));
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

Array::FindIndex(dinosaurs, EndsWithSaurus): 1

Array::FindIndex(dinosaurs, 2, EndsWithSaurus): 5

Array::FindIndex(dinosaurs, 2, 3, EndsWithSaurus): -1
 */

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.FindIndex(dinosaurs, EndsWithSaurus): {0}",
            Array.FindIndex(dinosaurs, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindIndex(dinosaurs, 2, EndsWithSaurus): {0}",
            Array.FindIndex(dinosaurs, 2, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): {0}",
            Array.FindIndex(dinosaurs, 2, 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.FindIndex(dinosaurs, EndsWithSaurus): 1

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

Array.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): -1
 */

open System

// Search predicate returns true if a string ends in "saurus".
let endsWithSaurus (s: string) =
    s.Length > 5 && s.Substring(s.Length - 6).ToLower() = "saurus"

let dinosaurs =
    [| "Compsognathus"; "Amargasaurus"
       "Oviraptor"; "Velociraptor"
       "Deinonychus"; "Dilophosaurus"
       "Gallimimus"; "Triceratops" |]

printfn ""
for dino in dinosaurs do
    printfn $"{dino}"

Array.FindIndex(dinosaurs, endsWithSaurus)
|> printfn "\nArray.FindIndex(dinosaurs, EndsWithSaurus): %i"

Array.FindIndex(dinosaurs, 2, endsWithSaurus)
|> printfn "\nArray.FindIndex(dinosaurs, 2, EndsWithSaurus): %i"

Array.FindIndex(dinosaurs, 2, 3, endsWithSaurus)
|> printfn "\nArray.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): %i"


// This code example produces the following output:
//
//     Compsognathus
//     Amargasaurus
//     Oviraptor
//     Velociraptor
//     Deinonychus
//     Dilophosaurus
//     Gallimimus
//     Triceratops
//
//     Array.FindIndex(dinosaurs, EndsWithSaurus): 1
//
//     Array.FindIndex(dinosaurs, 2, EndsWithSaurus): 5
//
//     Array.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): -1

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

FindIndex<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 first occurrence within the entire Array.

public:
generic <typename T>
 static int FindIndex(cli::array <T> ^ array, Predicate<T> ^ match);

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

static member FindIndex : 'T[] * Predicate<'T> -> int

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

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 first 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 forward starting at the first element and ending at the last 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>

FindIndex<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 first occurrence within the range of elements in the Array that extends from the specified index to the last element.

public:
generic <typename T>
 static int FindIndex(cli::array <T> ^ array, int startIndex, Predicate<T> ^ match);

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

static member FindIndex : 'T[] * int * Predicate<'T> -> int

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

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 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 first 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 forward starting at startIndex and ending at the last 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 startIndex to the end 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>

FindIndex<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 first occurrence within the range of elements in the Array that starts at the specified index and contains the specified number of elements.

public:
generic <typename T>
 static int FindIndex(cli::array <T> ^ array, int startIndex, int count, Predicate<T> ^ match);

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

static member FindIndex : 'T[] * int * int * Predicate<'T> -> int

Public Shared Function FindIndex(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

T[]

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

startIndex

Int32

The zero-based starting index of the 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 first 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 forward starting at startIndex and ending at startIndex plus count minus 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>