Array.Find

This C# method searches an array (with declarative syntax). We specify a Predicate type instance to determine what logic the search uses.

Finding notes

Array.Find allows us to use a for-loop without having to maintain loop indexes. It eases maintenance. We can also use FindLast and FindIndex.

Find example

This program shows how the Array.Find static method can be used on the Array type. This is a static method. It is found in the abstract base class for all array types.

using System;

// Use this array of string references.
string[] array1 = { "cat", "dog", "carrot", "bird" };

// Find first element starting with substring.
string value1 = Array.Find(array1,
    element => element.StartsWith("car", StringComparison.Ordinal));

// Find first element of three characters length.
string value2 = Array.Find(array1,
    element => element.Length == 3);

// Find all elements not greater than four letters long.
string[] array2 = Array.FindAll(array1,
    element => element.Length <= 4);

Console.WriteLine(value1);
Console.WriteLine(value2);
Console.WriteLine(string.Join(",", array2));
carrot
cat
cat,dog,bird

FindLast example

FindLast does the same thing as Find but searches from the final element. It proceeds backwards, searching each preceding element in order.

using System;

string[] array = { "dot", "net", "perls" };
// Find last string of length 3.
string result = Array.FindLast(array, s => s.Length == 3);
Console.WriteLine(result);
net

FindIndex example

Imperative searching of arrays is fast. But sometimes, a declarative method call to locate an index is useful. FindIndex and FindLastIndex are helpful.

using System;

// Use this input array.
int[] array = { 5, 6, 7, 6 };

// Use FindIndex method with predicate.
int index1 = Array.FindIndex(array, item => item == 6);
// Use LastFindIndex method with predicate.
int index2 = Array.FindLastIndex(array, item => item == 6);

// Write results.
Console.WriteLine("{0} = {1}", index1, array[index1]);
Console.WriteLine("{0} = {1}", index2, array[index2]);
1 = 6
3 = 6

Internals

Find does a forward linear search with a for-loop and tests each element with the Predicate. FindAll uses the List type and simply adds each match to this internal list variable.

The Predicate type is a generic type that encapsulates a method that must return a Boolean. We usually use the lambda syntax—but we can use an anonymous function.

We used Array.Find and Array.FindAll, which return a matching value or array when they succeed. These methods are static. They can be used with arrays of any element type.