โรงเรียนใดมีอาจารย์น้อยที่สุด?
Which school has the smallest amount of professors?
df_department = pd.DataFrame(columns=['school_code', 'dept_code']); df_professor = pd.DataFrame(columns=['dept_code'])
df_department.merge(df_professor, on='dept_code').groupby('school_code').size().idxmin()