How to use array_walk_recursive function in PHP to apply callback function to multi-dimensional array elements

In PHP, the array_walk_recursive function can be used to apply a callback function to all elements in a multidimensional array. This article will introduce how to use the array_walk_recursive function.

1. What is a multidimensional array

In PHP, arrays can be multidimensional, that is, one array can contain another array. For example, the following array is a two-dimensional array:

$array = array(
    array('name' => 'john', 'age' => 20),
    array('name' => 'mary', 'age' => 25)
);

2. array_walk_recursive function

array_walk_recursive function is used to apply a callback function to all elements in a multi-dimensional array. Its syntax is as follows:

array_walk_recursive ( array &$array , callable $callback [, mixed $userdata = NULL ] ) : bool

Parameter description:

• $array: the multidimensional array to be processed
• $callback: the callback function applied to the array elements
• $userdata: Optional user data, passed to the callback function

Returns true if successful, otherwise returns false.

3. Using the array_walk_recursive function

The following is an example of using the array_walk_recursive function. Suppose we have a multidimensional array containing the names and ages of users, and we want to add 10 to each age and print out each user's name and new age.

function add_age(&$item, $key) {
    if ($key == 'age') {
        $item += 10;
    }
}

$array = array(
    array('name' => 'john', 'age' => 20),
    array('name' => 'mary', 'age' => 25)
);

array_walk_recursive($array, 'add_age');

foreach ($array as $key => $value) {
    echo $value['name'] . ' ' . $value['age'] . '
';
}

In this example, we define a callback function add_age, which adds 10 to all ages. We then pass this callback function to the array_walk_recursive function, passing it our multidimensional array. Finally, we use a foreach loop to print out each user's name and new age.

4. Summary

The array_walk_recursive function can easily apply a callback function to all elements in a multidimensional array. It is very useful when dealing with multi-level nested arrays, which can avoid writing a lot of repeated code. We can use this function to complete various operations, such as data filtering, conversion, etc.

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