Fastest way to add prefix to array keys?

Question

What is the fastest way to add string prefixes to array keys?

Input

$array = array(
 \'1\' => \'val1\',
 \'2\' => \'val2\',
);

<

Answer 1

function array_key_prefix_suffix(&$array,$prefix='',$suffix=''){
        $key_array = array_keys($array);
        $key_string = $prefix.implode($suffix.','.$prefix,$key_array).$suffix;
        $key_array = explode(',', $key_string);
        $array = array_combine($key_array, $array);
    }

This is implemented and working very well