- array_map: documentation ( source)
- array_combine: documentation ( source)
- print_r: documentation ( source)
- array_keys: documentation ( source)
<?php
$array=array("a"=>aaa,"b"=>aaaaadddd);
$array = array_combine(array_map(function($k){ return 'prefix'.$k; }, array_keys($array)) , $array );
echo "<pre>";print_r($array);