// changes all array keys to keys with prefix

array_keys_prefix.php

<?php

$a = array('a1'=>'1','a2'=>2);

// changes all array keys to keys with prefix
$prefix = 'page_';
$a = array_combine(explode(',', $prefix.implode(','.$prefix, array_keys($a))), array_values($a));
 
print_r($a);
/*
Array
(
    [page_a1] => 1
    [page_a2] => 2
)
*/
?>