PHP数组比较有关问题

$ar1=array(array('id'=>1,"name"=>"张1","sign"=>""),array('id'=>2,"name"=>"张2","sign"=>""),array('id'=>5,"name"=>"张5","sign"=>""));
        $ar2=array(array('id'=>1,"name"=>"张1"),array('id'=>2,"name"=>"张2"));

$ar1=array(array('id'=>1,"name"=>"张1","sign"=>""),array('id'=>2,"name"=>"张2","sign"=>""),array('id'=>5,"name"=>"张5","sign"=>""));
$ar2=array(array('id'=>1,"name"=>"张1"),array('id'=>2,"name"=>"张2"));

//先将 $ar2 规格化一下
foreach($ar2 as $v) $r[$v['id']] = $v;
$ar2 = $r;

//接下来就简单了
foreach($ar1 as &$v) {
  if(isset($ar2[$v['id']])) $v['sign'] = 1;
}

print_r($ar1);

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => 张1
            [sign] => 1
        )

    [1] => Array
        (
            [id] => 2
            [name] => 张2
            [sign] => 1
        )

    [2] => Array
        (
            [id] => 5
            [name] => 张5
            [sign] => 
        )

)