PHP在多维数组中搜索项目

foreach($arrays as $arr){
  if($arr[\'NUM\']==$num){
    return $arr[\'DESC\'];
  }
}

$u_id= array(
     \'2770\' => \'description one\',
     \'33356\' => \'description two\',
     \'13576\' => \'description three\',
     \'14141\' => \'description four\'
);

$u_id[2770]

$u_id= array(
    \'2770\' => array(
        NUM=>\'2770\', DESC=>\'description one\'
    ), 

    \'33356\' => array(
        NUM=>\'33356\', DESC=>\'description two\'
    ), 

    \'13576\' => array(
        NUM=>\'13576\', DESC=>\'description three\'
    ),

    \'14141\' => array(
        NUM=>\'14141\', DESC=>\'description four\'
    )
);

$u_id[2770][\"NUM\"]