$arr1 = array(
    'a' => '42','b' => '551','c' => '512','d' => 'gge',) ;


$arr2 = array(
    'd' => 'ordered','b' => 'is','c' => 'now','a' => 'this',) ;

$arr2ordered = array() ;

foreach (array_keys($arr1) as $key) {
    $arr2ordered[$key] = $arr2[$key] ;
}