Merges 2 arrays properly

array_deep_merge.php

<?php

/*
 * Merges two arrays and takes multi-dimensional arrays into account.
 *
 * @param  array  $original
 * @param  array  $merging
 * @return array
 */
function array_deep_merge(array $original, array $merging): array
{
    $array = array_merge($original, $merging);

    foreach ($original as $key => $value) {
        if (! is_array($value)) {
            continue;
        }

        if (! array_key_exists($key, $merging)) {
            continue;
        }

        if (is_numeric($key)) {
            continue;
        }

        $array[$key] = array_deep_merge($value, $merging[$key]);
    }

    return $array;
}