Recursive functions, I can never find exactly what I need in a pinch

combos.php

<?php

function combos($data, &$all = array(), $group = array(), $val = null, $i = 0) {
    if (isset($val)) {
        array_push($group, $val);
    }
    if ($i >= count($data)) {
        array_push($all, $group);
    } else {
        foreach ($data[$i] as $v) {
            combos($data, $all, $group, $v, $i + 1);
        }
    }
    return $all;
}

$data = array(
    array('a', 'b'),
    array('e', 'f', 'g'),
    array('w', 'x', 'y', 'z'),
);

$combos = combos($data);

echo '<pre>'; print_r($combos); echo '</pre>';

output.txt

Array
(
    [0] => Array
        (
            [0] => a
            [1] => e
            [2] => w
        )
 
    [1] => Array
        (
            [0] => a
            [1] => e
            [2] => x
        )
 
    [2] => Array
        (
            [0] => a
            [1] => e
            [2] => y
        )
 
    [3] => Array
        (
            [0] => a
            [1] => e
            [2] => z
        )
 
    [4] => Array
        (
            [0] => a
            [1] => f
            [2] => w
        )
 
    [5] => Array
        (
            [0] => a
            [1] => f
            [2] => x
        )
 
    [6] => Array
        (
            [0] => a
            [1] => f
            [2] => y
        )
 
    [7] => Array
        (
            [0] => a
            [1] => f
            [2] => z
        )
 
    [8] => Array
        (
            [0] => a
            [1] => g
            [2] => w
        )
 
    [9] => Array
        (
            [0] => a
            [1] => g
            [2] => x
        )
 
    [10] => Array
        (
            [0] => a
            [1] => g
            [2] => y
        )
 
    [11] => Array
        (
            [0] => a
            [1] => g
            [2] => z
        )
 
    [12] => Array
        (
            [0] => b
            [1] => e
            [2] => w
        )
 
    [13] => Array
        (
            [0] => b
            [1] => e
            [2] => x
        )
 
    [14] => Array
        (
            [0] => b
            [1] => e
            [2] => y
        )
 
    [15] => Array
        (
            [0] => b
            [1] => e
            [2] => z
        )
 
    [16] => Array
        (
            [0] => b
            [1] => f
            [2] => w
        )
 
    [17] => Array
        (
            [0] => b
            [1] => f
            [2] => x
        )
 
    [18] => Array
        (
            [0] => b
            [1] => f
            [2] => y
        )
 
    [19] => Array
        (
            [0] => b
            [1] => f
            [2] => z
        )
 
    [20] => Array
        (
            [0] => b
            [1] => g
            [2] => w
        )
 
    [21] => Array
        (
            [0] => b
            [1] => g
            [2] => x
        )
 
    [22] => Array
        (
            [0] => b
            [1] => g
            [2] => y
        )
 
    [23] => Array
        (
            [0] => b
            [1] => g
            [2] => z
        )
)

This function is not useful in case of maintaining the key too. like if input is
$data = array(
array('11'=>'a', '22' => 'b'),
array('33' => 'e', '44' => 'f'),
);

It will not return the key as is.