ค้นหาจำนวนห้องที่ไม่มีการจองใดๆ
Find the number of rooms that do not have any reservation.
df_rooms = pd.DataFrame(columns=['roomid', 'room']); df_resv = pd.DataFrame(columns=['roomid', 'room'])
df_rooms[~df_rooms['roomid'].isin(df_resv['room'])]['roomid'].count()