คนไข้ที่นัดครั้งล่าสุดชื่ออะไร?
What is the name of the patient who made the most recent appointment?
df_patient = pd.DataFrame(columns = ['name', 'ssn']); df_appointment = pd.DataFrame(columns = ['patient', 'start'])
df = df_appointment.sort_values('start', ascending=False); df_patient[df_patient['ssn'] == df['patient'].iloc[0]]['name']