<?php
/**
 * Convert keys in an array.
 * 
 * @param array $array Source data
 * @param callable $callback Function name (strtolower, strtoupper, ucfirst, lcfirst, ucwords)
 * @return array
 */
function array_convert_key_case(array $array, callable $callback = 'strtolower')
{
    return array_combine(
        array_map($callback, array_keys($array)),
        array_values($array)
    );
}
?>