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

I figured out one-line solution:

array_walk($array, create_function('$value, &$key', '$key = "prefix" . $key;'));

Answer 2

Could do this in one long line I presume:

$array = array_combine(
    array_map(function($k){ return 'prefix'.$k; }, array_keys($array)),
    $array
);

Or for versions of PHP prior to 5.3:

$array = array_combine(
    array_map(create_function('$k', 'return "prefix".$k;'), array_keys($array)),
    $array
);

There's probably dozens of ways to do this though:

foreach ($array as $k => $v)
{
    $array['prefix_'.$k] = $v;
    unset($array[$k]);
}

Answer 3

function keyprefix($keyprefix, Array $array) {

    foreach($array as $k=>$v){
        $array[$keyprefix.$k] = $v;
        unset($array[$k]);
    }

    return $array; 
}

Using array_flip will not preserve empty or null values. Additional code could be added in the unlikely event that the prefixed key already exists.