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

Another way to do achieve is with array_flip()

 &$val) { $val = "prefix" . $val; }
    $data = array_flip($data);