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Array.ForEach Method ExamplesUse the Array.ForEach method with an array of objects, calling a method on every element.
C#
This page was last reviewed on Apr 24, 2022.
Array.ForEach. This C# method loops over every element. It calls another method on each element in an array. ForEach() is a declarative syntax form—this simplifies certain code patterns.
Shows a method
Usually the Array.ForEach method is mostly used on arrays of objects. Each object has a method we want to invoke, and we use a lambda to call that method.
Array
Lambda
Class example. Here we create an array of class instances with an initializer expression. Each Dog object has an Add() method that we want to call.
Array We create an array of Dog instances, and set the Size of each dog to a certain integer.
ForEach The ForEach method calls the lambda (second argument) on each Dog instance we created. Each Dog's size is incremented.
Shows a method
using System; using System.Collections.Generic; class Dog { public int Size { get; set; } public void Add() { this.Size++; } } class Program { static void Main() { // Create array of objects. var dogs = new Dog[]{ new Dog(){ Size = 1 }, new Dog(){ Size = 3 } }; // Call method on each object. Array.ForEach(dogs, dog => dog.Add()); Console.WriteLine("DONE"); } }
DONE
Console example. Next we call Array.ForEach on an int array. We cannot modify values within the array, but we can act upon them or pass them to a Console static method.
Int Array
Action The Action type (the second argument in ForEach) returns no value: it is void. It cannot directly modify elements.
Action
using System; class Program { static void Main() { int[] items = { 10, 100, 1000 }; // Display elements with ForEach. Array.ForEach(items, element => Console.WriteLine( "Element is " + element)); } }
Element is 10 Element is 100 Element is 1000
Jagged array example. ForEach uses an Action type as its second argument. We can modify elements in nested jagged arrays with Array.ForEach.
Here This example program shows how to allocate a jagged array and then apply the Array.ForEach method with 2 arguments.
Jagged Arrays
Arguments The arguments are the array itself, and a lambda expression that represents an Action type instance.
Lambda The left part before the => token is the argument name, and the right part is the expression taken upon the argument.
Lambda
Info The first array element in each subarray is modified. Usually, with ForEach, this style of code is not helpful.
using System; class Program { static void Main() { // Allocate a jagged array and put 3 subarrays into it. int[][] array = new int[3][]; array[0] = new int[2]; array[1] = new int[3]; array[2] = new int[4]; // Use ForEach to modify each subarray's first element. // ... Because the closure variable is an array reference, // you can change it. Array.ForEach(array, subarray => subarray[0]++); foreach (int[] subarray in array) { foreach (int i in subarray) { Console.Write(i); } Console.WriteLine(); } // Apply the same routine with ForEach again. Array.ForEach(array, subarray => subarray[0]++); foreach (int[] subarray in array) { foreach (int i in subarray) { Console.Write(i); } Console.WriteLine(); } } }
10 100 1000 20 200 2000
Discussion. The Action delegate receives a formal parameter list. These arguments are copied by value. When we copy an element of an array as a parameter, it becomes a scalar variable.
So With ForEach, we cannot directly modify array elements. The change is not reflected in the array.
Thus Array.ForEach is not a "map" method. It is a loop abstraction, but not a good way to mutate every array element.
ToArray A LINQ query, with the ToArray method, is an easier way to create a modified array.
ToArray
A summary. Array.ForEach is a declarative loop. By applying this method, we can invoke a method on each array element. Or we can modify something based on a reference (class) element.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Apr 24, 2022 (edit link).
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