ประเทศใดมีอย่างน้อย 3 เมือง?
Which countries have at least 3 cities?
df = pd.DataFrame(columns=['country_id', 'country'])
df_city = pd.DataFrame(columns=['country_id'])
df[df['country_id'].isin(df_city['country_id'].value_counts()[df_city['country_id'].value_counts() >= 3].index)]['country']