$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);