ไม่รวมผลิตภัณฑ์จำนวนเท่าใดในคำสั่งซื้อใด ๆ
How many products were not included in any order?
products = pd.DataFrame(columns=['product_id']); df = pd.DataFrame(columns=['product_id'])
products[~products['product_id'].isin(df['product_id'])].count()