Find Method
.NET Framework Class Library
List<(Of <(T>)>)..::.Find Method

Searches for an element that matches the conditions defined by the specified predicate, and returns the first occurrence within the entire List<(Of <(T>)>).

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)
 Syntax
Visual Basic (Declaration) 
Public Function Find ( _
    match As Predicate(Of T) _
) As T
Visual Basic (Usage) 
Dim instance As List
Dim match As Predicate(Of T)
Dim returnValue As T

returnValue = instance.Find(match)
C# 
public T Find(
    Predicate<T> match
)
Visual C++ 
public:
T Find(
    Predicate<T>^ match
)
JScript 
public function Find(
    match : Predicate<T>
) : T

Parameters

match
Type: System..::.Predicate<(Of <(T>)>)
The Predicate<(Of <(T>)>) delegate that defines the conditions of the element to search for.

Return Value

Type: T
The first element that matches the conditions defined by the specified predicate, if found; otherwise, the default value for type T.
 Exceptions
ExceptionCondition
ArgumentNullException

match is nullNothingnullptra null reference (Nothing in Visual Basic).
 Remarks

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 the current List<(Of <(T>)>) are individually passed to the Predicate<(Of <(T>)>) delegate, moving forward in the List<(Of <(T>)>), starting with the first element and ending with the last element. Processing is stopped when a match is found.

Important noteImportant Note:

When searching a list containing value types, make sure the default value for the type does not satisfy the search predicate. Otherwise, there is no way to distinguish between a default value indicating that no match was found and a list element that happens to have the default value for the type. If the default value satisfies the search predicate, use the FindIndex method instead.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.
 Examples

The following code example demonstrates the Find, FindLast, and FindAll methods. A List<(Of <(T>)>) 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 Find method traverses the list from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element "Amargasaurus".

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 FindLast method is used to search the list backward from the end. It finds the element "Dilophosaurus" at position 5. The FindAll method is used to return a List<(Of <(T>)>) containing all the elements that end in "saurus". The elements are displayed.

Finally, the RemoveAll method is used to remove all entries ending with "saurus", and the Exists method shows that all such strings are gone.

Visual Basic 
Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)

        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Amargasaurus")
        dinosaurs.Add("Oviraptor")
        dinosaurs.Add("Velociraptor")
        dinosaurs.Add("Deinonychus")
        dinosaurs.Add("Dilophosaurus")
        dinosaurs.Add("Gallimimus")
        dinosaurs.Add("Triceratops")

        Console.WriteLine()
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

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

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

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

        Console.WriteLine(vbLf & _
            "FindAll(AddressOf EndsWithSaurus):")
        Dim sublist As List(Of String) = _
            dinosaurs.FindAll(AddressOf EndsWithSaurus)

        For Each dinosaur As String In sublist
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & _
            "{0} elements removed by RemoveAll(AddressOf EndsWithSaurus).", _
            dinosaurs.RemoveAll(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & "List now contains:")
        For Each dinosaur As String In dinosaurs
            Console.WriteLine(dinosaur)
        Next

        Console.WriteLine(vbLf & _
            "Exists(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.Exists(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
'
'TrueForAll(AddressOf EndsWithSaurus: False
'
'Find(AddressOf EndsWithSaurus): Amargasaurus
'
'FindLast(AddressOf EndsWithSaurus): Dilophosaurus
'
'FindAll(AddressOf EndsWithSaurus):
'Amargasaurus
'Dilophosaurus
'
'2 elements removed by RemoveAll(AddressOf EndsWithSaurus).
'
'List now contains:
'Compsognathus
'Oviraptor
'Velociraptor
'Deinonychus
'Gallimimus
'Triceratops
'
'Exists(AddressOf EndsWithSaurus): False
C# 
using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        List<string> dinosaurs = new List<string>();

        dinosaurs.Add("Compsognathus");
        dinosaurs.Add("Amargasaurus");
        dinosaurs.Add("Oviraptor");
        dinosaurs.Add("Velociraptor");
        dinosaurs.Add("Deinonychus");
        dinosaurs.Add("Dilophosaurus");
        dinosaurs.Add("Gallimimus");
        dinosaurs.Add("Triceratops");

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nTrueForAll(EndsWithSaurus): {0}",
            dinosaurs.TrueForAll(EndsWithSaurus));

        Console.WriteLine("\nFind(EndsWithSaurus): {0}", 
            dinosaurs.Find(EndsWithSaurus));

        Console.WriteLine("\nFindLast(EndsWithSaurus): {0}",
            dinosaurs.FindLast(EndsWithSaurus));

        Console.WriteLine("\nFindAll(EndsWithSaurus):");
        List<string> sublist = dinosaurs.FindAll(EndsWithSaurus);

        foreach(string dinosaur in sublist)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine(
            "\n{0} elements removed by RemoveAll(EndsWithSaurus).", 
            dinosaurs.RemoveAll(EndsWithSaurus));

        Console.WriteLine("\nList now contains:");
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine("\nExists(EndsWithSaurus): {0}", 
            dinosaurs.Exists(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

TrueForAll(EndsWithSaurus): False

Find(EndsWithSaurus): Amargasaurus

FindLast(EndsWithSaurus): Dilophosaurus

FindAll(EndsWithSaurus):
Amargasaurus
Dilophosaurus

2 elements removed by RemoveAll(EndsWithSaurus).

List now contains:
Compsognathus
Oviraptor
Velociraptor
Deinonychus
Gallimimus
Triceratops

Exists(EndsWithSaurus): False
 */
Visual C++ 
using namespace System;
using namespace System::Collections::Generic;

// 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()
{
    List<String^>^ dinosaurs = gcnew List<String^>();

    dinosaurs->Add("Compsognathus");
    dinosaurs->Add("Amargasaurus");
    dinosaurs->Add("Oviraptor");
    dinosaurs->Add("Velociraptor");
    dinosaurs->Add("Deinonychus");
    dinosaurs->Add("Dilophosaurus");
    dinosaurs->Add("Gallimimus");
    dinosaurs->Add("Triceratops");

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

    Console::WriteLine("\nTrueForAll(EndsWithSaurus): {0}",
        dinosaurs->TrueForAll(gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nFind(EndsWithSaurus): {0}", 
        dinosaurs->Find(gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nFindLast(EndsWithSaurus): {0}",
        dinosaurs->FindLast(gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nFindAll(EndsWithSaurus):");
    List<String^>^ sublist = 
        dinosaurs->FindAll(gcnew Predicate<String^>(EndsWithSaurus));

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

    Console::WriteLine(
        "\n{0} elements removed by RemoveAll(EndsWithSaurus).", 
        dinosaurs->RemoveAll(gcnew Predicate<String^>(EndsWithSaurus)));

    Console::WriteLine("\nList now contains:");
    for each(String^ dinosaur in dinosaurs)
    {
        Console::WriteLine(dinosaur);
    }

    Console::WriteLine("\nExists(EndsWithSaurus): {0}", 
        dinosaurs->Exists(gcnew Predicate<String^>(EndsWithSaurus)));
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

TrueForAll(EndsWithSaurus): False

Find(EndsWithSaurus): Amargasaurus

FindLast(EndsWithSaurus): Dilophosaurus

FindAll(EndsWithSaurus):
Amargasaurus
Dilophosaurus

2 elements removed by RemoveAll(EndsWithSaurus).

List now contains:
Compsognathus
Oviraptor
Velociraptor
Deinonychus
Gallimimus
Triceratops

Exists(EndsWithSaurus): False
 */
 Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
 Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
 See Also

Reference

List<(Of <(T>)>) Class
List<(Of <(T>)>) Members
System.Collections.Generic Namespace
Exists
FindLast
FindAll
FindIndex
FindLastIndex
BinarySearch
IndexOf
LastIndexOf
Predicate<(Of <(T>)>)
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Not much good if you don't want to search for ends with saurus.      UKCodeMonkey ... Todd Girvin   |   Edit   |   Show History

If you want to find a dinosaur that ends with a different name, which you don't want a function hard coded for as in the above example, use a delegate:

Instead of :

dinosaurs.Find(EndsWithSaurus));


You would use a delegate and write:

dinosaurs.Find(delegate(string s) { return search.EndsWith(s); }));


This matches items in the array that end with the string specified by search.

Another delegate      kdriedge   |   Edit   |   Show History
In the Console.WriteLines I added the following:
            Console.WriteLine("\nFind(delegate): {0}",
                dinosaurs.Find(delegate(string s) { return s.EndsWith("saurus"); }));

Delegates are great      turanj   |   Edit   |   Show History
Great code samples UKCodeMonkey and Kdriedge. I was about to use this example by promoting a variable from local to class scope. Using delegates is a much more elegant solution. I will have to learn how to use them better.

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What about more complex types?      sebastian gomez   |   Edit   |   Show History

In case you have a more complex type, let's say a Dinosaur class, and your list is no longer a list of strings but a list of Dinosaurs:

List<Dinosaur> dinosaurs = new List<Dinosaur>();


and you want to find a specific dinosaur (which you already know the name) you should use a delegate like the following:

dinosaurs.Find(delegate(Dinosaur dino) {return dino.Name == name;});


where name is a local variable containing the name you're looking for.

Hope this helps someone, examples in this page were too simple.

A clearer illustration with FindIndex and Find using delegates      Aldo Salzberg   |   Edit   |   Show History
I put some examples on the Find vs. FindIndex methods including objects on the FindIndex entry on the following:

http://msdn.microsoft.com/en-us/library/x1xzf2ca.aspx

http://aldosalzberg.wordpress.com/2009/09/24/using-find-in-net-collections-generics-lists/

Thanks,

Aldo
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Lambda      LukeSkywalker   |   Edit   |   Show History

Even more concise code can be achieved by using Lambda expressions instead of delegates. I've made/assumed the collection is now strongly typed, containing a made up Dinosaur type.

  
var compare = new Dinosaur(DinoTypes.Jaffinkisaurus); // fictitious enum.

  
dinosaurs.Find(dino => dino.Type == compare.Type); // => is special Lambda syntax.



The Lambda is executed for each item in the collection. Each item becomes the dino variable. I suggest looking at Lambdas if only so you understand when you see other people's code.

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