PHP array_walk_recursive() with Examples

Current PHP usage

array_walk_recursive() applies a callback to every non-array value inside a nested array. It descends through nested arrays automatically.

$data = ['a' => 1, 'group' => ['b' => 2]];
array_walk_recursive($data, function (&$value) {
    $value *= 10;
});
print_r($data);

The callback receives leaf values; nested arrays themselves are not passed to it as leaf values.

The array_walk_recursive() function in PHP applies a user-defined callback function to each element of an array, including elements in nested arrays. It's useful for traversing multi-dimensional arrays.

Syntax

array_walk_recursive(array $array, callable $callback, mixed $userdata = null): bool

Example 1: Simple Array

function display($value, $key) {
    echo "$key: $value <BR>";
}
$array = ['a' => 1, 'b' => 2];
array_walk_recursive($array, 'display');

a: 1 
b: 2

Example 2: Nested Array

function display($value, $key) {
    echo "$key: $value <BR>";
}
$array = [
    'a' => 1, 
    'b' => ['c' => 2, 'd' => 3]
];
array_walk_recursive($array, 'display');

a: 1 
c: 2 
d: 3

Example 3: Using Userdata

$array = [
    'a' => 1, 
    'b' => ['c' => 2, 'd' => 3]
];

$prefix = "Prefix";

array_walk_recursive($array, function($value, $key) use ($prefix) {
    echo "$prefix $key: $value <br>";
});

Prefix a: 1 
Prefix c: 2 
Prefix d: 3

Difference between array_walk_recursive() and array_walk():

array_walk():
Operates only on the top-level elements of an array.
Does not iterate over nested arrays.

array_walk_recursive(): Operates on all elements, including nested arrays.
Recursively applies the callback to each element.

Use array_walk() for flat arrays and array_walk_recursive() for multi-dimensional arrays where nested elements need to be processed.

Conclusion

The array_walk_recursive() function is essential when processing nested arrays, as it allows the application of a callback to each element, regardless of the array’s depth.
To check the variable is array or not array_walk()
Array REFERENCE

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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