This function will extract keys from a multidimensional array

<?php
function multiarray_keys($ar) {
            
    foreach($ar as $k => $v) {
        $keys[] = $k;
        if (is_array($ar[$k]))
            $keys = array_merge($keys, multiarray_keys($ar[$k]));
    }
    return $keys;
}
?>

Example code:

<?php
$array = array("color" => array("1stcolor" => "blue", "2ndcolor" => "red", "3rdcolor" => "green"),
               "size"  => array("small", "medium", "large"));

echo "<pre>";
print_r($array);
echo "</pre>";

echo "<pre>";
print_r(multiarray_keys($array));
echo "</pre>";
?>

Example output:

Array
(
    [color] => Array
        (
            [1stcolor] => blue
            [2ndcolor] => red
            [3rdcolor] => green
        )

    [size] => Array
        (
            [0] => small
            [1] => medium
            [2] => large
        )

)

Array
(
    [0] => color
    [1] => 1stcolor
    [2] => 2ndcolor
    [3] => 3rdcolor
    [4] => size
    [5] => 0
    [6] => 1
    [7] => 2
)