$arr[] = array('name'=>'a','flag'=>1);
$arr[] = array('name'=>'b','flag'=>2);
$arr[] = array('name'=>'a','flag'=>1);
$flag=array();
foreach($arr as $arr2){
    $flag[]=$arr2["flag"];
    }
array_multisort($flag, SORT_ASC, $arr);
print_r($arr);