USPS จัดส่งเอกสารจำนวนเท่าใด
How many documents were shipped by USPS?
df_documents = pd.DataFrame(columns=['Id', 'shipping_agent_code']); df_agents = pd.DataFrame(columns=['Id', 'shipping_agent_name'])
(df_documents['shipping_agent_code'].isin(df_agents[df_agents['shipping_agent_name'] == 'USPS']['Id'])).sum()