array_map_recursive.php

<?php

function array_map_recursive($f, $xs) {
    $out = [];
    foreach ($xs as $k => $x) {
        $out[$k] = (is_array($x)) ? array_map_recursive($f, $x) : $f($x);
    }
    return $out;
}

$data = [
    'foo' => [
        'bar' => [
            'baz' => [
                'rofl',
                'omg',
                'wtf',
            ],
        ],
    ],
];

var_dump(array_map_recursive('strtoupper', $data));