function array_order(&$ar, $by) {
  asort($by);
  foreach($by as $k=>$v) {
    $r[$k] = $ar[$k];
  }
  return $ar = $r;
}

$arr = array(
  'a' => 'aa',
  'b' => 'bb',
  'c' => 'cc',
);

$sort_by = array(
  'a' => 2,
  'b' => 3,
  'c' => 1,
);

array_order($arr, $sort_by);

print_r($arr);

------解决方案--------------------
array_multisort($sort_by,SORT_ASC,$arr);
print_r($arr);