PHP array_walk_recursive() with Examples

array_walk_recursive(): traversing multi-dimensional array

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 
";
}
$array = [
    'a' => 1, 
    'b' => ['c' => 2, 'd' => 3]
];
array_walk_recursive($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 
";
});

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

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