List.Find Method
Assembly: mscorlib (in mscorlib.dll)
public T Find ( Predicate<T> match )
public function Find ( match : Predicate<T> ) : T
Not applicable.
Parameters
- match
The Predicate delegate that defines the conditions of the element to search for.
Return Value
The first element that matches the conditions defined by the specified predicate, if found; otherwise, the default value for type T.The Predicate 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 are individually passed to the Predicate delegate, moving forward in the List, starting with the first element and ending with the last element. Processing is stopped when a match is found.
 Important: |
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| 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.
The following code example demonstrates the Find, FindLast, and FindAll methods. A List 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".
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| 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 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.
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 */
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.