PHP array_map Function | Modify Array In PHP

Using loops is one of the most basic concepts taught to a novice programmer. We always come up with a loop solution for any trivial task because we are accustomed to them. However, a more experienced programmer might write a solution without actually looping through the array using an inbuilt defined function. The PHP array_map function is an inbuilt PHP function that sends the array elements to a user-defined function.

In this article, I will discuss the PHP array_map Function to modify the array in PHP.

What Is array_map Function?

array_map — Applies the callback to the elements of the given arrays

http://php.net

The PHP array_map function is an inbuilt PHP function that sends the array elements to a user-defined function. It helps to modify the contents of an array using the user-defined function and returns the modified array as output.

Syntax

array_map(callbackFunction,arr1,arr2…)

Parameters

The array_map function takes in two mandatory parameters; callbackFunction and an array. The rest of the parameters are optional.

• callbackFunction: The callback Function is a mandatory user-defined function passed to the array_map function according to which the array elements will be modified.
• $arr1: The array arr1 is a mandatory array which will be modified by the callback function.
• $arr2..$arrn: You can pass more than one array to the PHP array_map Function.

Examples

Let’s consider the following examples to understand more.

Example 1: Basic Usage with Integers

If you need to calculate the squares of all the numbers given in an array, this is what you might possibly code using a foreach loop:

<?php
	$testNum = array(1,2,3,4,5);
	foreach($testNum as $key => $num) {
		$testNum[$key] = $num*$num;
	}
	print_r($testNum);
	/* Output:
		Array
		(
		    [0] => 1
		    [1] => 4
		    [2] => 9
		    [3] => 16
		    [4] => 25
		)
	*/
?>

The array_map function can be used to implement the same solution as follows:

<?php
	
	function calculateSquares($num) {
		return $num*$num;
	}
	
	$testNum = array(1,2,3,4,5);
	$testNum = array_map('calculateSquares', $testNum);
	print_r($testNum);
	/* Output:
		Array
		(
		    [0] => 1
		    [1] => 4
		    [2] => 9
		    [3] => 16
		    [4] => 25
		)
	*/
?>

We can also use Lambda Functions to implement the same logic as shown below:

<?php
	$lambdaFunc = function($num) {
		return $num * $num;
	};
	
	$testNum = array(1,2,3,4,5);
	$testNum = array_map($lambdaFunc, $testNum);
	print_r($testNum);
	/*
	Array
		(
		    [0] => 1
		    [1] => 4
		    [2] => 9
		    [3] => 16
		    [4] => 25
		)
	*/
?>

Example 2: Calling a Class Method

If the method you are calling is a class method, then you can use the array_map function by passing the object reference with the method name as shown in the following example:

<?php

	class TestArrayMap {

		private function calculateSquares($num) {
			return $num * $num;
		}

		public function getSquares($testNumArray) {
                        //Object reference passed along with method name
			return array_map(array($this, 'calculateSquares'), $testNumArray);
		}

	}

	$testArrayMapObj = new TestArrayMap();
	print_r($testArrayMapObj->getSquares(array(1,2,3,4,5)));
?>

Example 3: Pre Defined PHP Functions

You may also pass PHP predefined functions as the callback method instead of creating user-defined functions. Here, we are calling the inbuilt PHP strtoupper Function.

<?php
	$stringArray = array('bringing', 'knowledge', 'together');
	$upperCaseArray = array_map('strtoupper', $stringArray);
	print_r($upperCaseArray);
	/*
		Array
		(
		    [0] => BRINGING
		    [1] => KNOWLEDGE
		    [2] => TOGETHER
		)
	*/
?>

Example 4: Null Callback

On passing null as the callback function, array_map merges two arrays in the following way:

<?php
	$userNames = array('Vishesh', 'Sam', 'Joe');
	$userEmails = array('[email protected]', '[email protected]', '[email protected]');
	print_r(array_map(null, $userNames, $userEmails));
	/*
	Array
	(
	    [0] => Array
	        (
	            [0] => Vishesh
	            [1] => [email protected]
	        )

	    [1] => Array
	        (
	            [0] => Sam
	            [1] => [email protected]
	        )

	    [2] => Array
	        (
	            [0] => Joe
	            [1] => [email protected]
	        )

	)
	*/
?>

Performance Analysis

You might be wondering is a for loop is faster than using the PHP array_map function in terms of processing time. I performed a performance analysis on PHP 7.2 and found that the PHP array_map Function has almost the same performance as a regular for loop.

I performed the analysis by calculating the time required to calculate squares of all numbers from 1 to 1000000 using both array_map and a foreach loop. The code I used for calculting time difference is as follows:

<?php
	/* ############## Array Map ################### */
	function calculateSquares($num) {
		return $num*$num;
	}
	$startTime = microtime(true);
	$testNum = range(1,1000000);
	$newArr = array_map('calculateSquares', $testNum);
	$endTime = microtime(true);
	echo 'Time Taken By array_map: '.($endTime - $startTime);

        /* ############## For Loop #################### */
	$startTimeLoop = microtime(true);
	$testNum = range(1,1000000);
	$newArr = array();
	foreach($testNum as $key => $value) {
		$newArr[] = $value * $value;
	}
	$endTimeLoop = microtime(true);
	echo '<br/>Time Taken by Loop: '.($endTimeLoop - $startTimeLoop);
?>

As shown in the above test results the PHP array_map Function almost performs equally good as a regular foreach loop for performing the same task. However, using array_map looks better in the source code. It reduces the number of for-loops you have to write and performs the same task.

Conclusion

In this article, we discussed the use of PHP array_map function for modifying elements in an array. I also did a performance analysis for checking the time taken by a traditional for loop and using the array_map function.

You can also read more about array_map function on the official PHP documentation. Please read more articles on PHP on Concatly. Kindly leave your valuable comments below to help me improve this resource.