array_walk to apply user function to elements of an array in PHP

Current PHP usage

array_walk() calls a function for every element in an array and can modify values by reference. It is intended for side-effect processing rather than building a separate result array.

$names = ['ana', 'ben'];
array_walk($names, function (&$value) {
    $value = strtoupper($value);
});
print_r($names);

Use array_map() when the goal is to produce a transformed array from return values instead of modifying elements in place.

We can create our own function and pass each element of an array through the function.

array_walk(input_array, function, optional_extra_parameter )

Return Value ( boolean ): TRUE on success or FALSE on failure

Let us try this with an example. We will try to add one char 'x' to each element of an array

<?Php
function add_char($str){
$str = $str.'x';
echo $str.'<br>';
}
$a= array(1,2,v,4,7.3,105 ); 

array_walk($a, 'add_char');
?>

The output is here

1x
2x
vx
4x
7.3x
105x

The function array_walk returns TRUE or FALSE based on the success or failure. It does not return a new array with modified elements. You can add the following lines to test your script.

<?Php
function add_char($str){
$str = $str.'x';
echo $str.'<br>';
}
$a= array(1,2,v,4,7.3,105 ); 

if(array_walk($a, 'add_char')){
echo " Success ";
}else{
echo " Failed";
}
?>

The output is here

1x
2x
vx
4x
7.3x
105x
<b>Success</b>

To get a new array with modified elements then we have to use array_map function.

array_walk with optional parameter

function my_function(&$value,$key,$v1){
$value=$value*$v1;
}

$a= array('First'=>1,'Second'=>2,'Third'=>3 ); 

if(array_walk($a, 'my_function',2)){
echo "  Success <br> ";
}else{
echo " Failed <br>";
}
print_r($a);

Output is here

Success
Array ( [First] => 2 [Second] => 4 [Third] => 6 )

Example : Using `array_walk()` to Transform Array Data

This example demonstrates modifying each element in an array using array_walk() to format data. Here, we append a unit to each numeric value.

<?php
$prices = [100, 200, 300];
array_walk($prices, function(&$value) {
    $value = "$" . $value . ".00";  // Append currency format
});
print_r($prices);
?>

Output:

Array ( [0] => $100.00 [1] => $200.00 [2] => $300.00 )

Difference between array_map and array_walk

Detail	array_map	array_walk
output array element	Input array values remain same	Input array values updated
return value	New array	Boolean: True or False
Input Number of arrays	One or more	One only
Extra Parameter	No	Yes

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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array_walk(): applies a user-defined callback function to each element in an array