Pandas groupby在进行均值和排序后保留所有列

Question

我有以下数据框，

Input Dataframe

      class  section  sub  marks  school  city
0     I      A        Eng  80     jghss   salem
1     I      A        Mat  90     jghss   salem 
2     I      A        Eng  50     Nan     salem 
3     III    A        Eng  80     gphss   Nan
4     III    A        Mat  45     Nan     salem
5     III    A        Eng  40     gphss   Nan
6     III    A        Eng  20     gphss   salem
7     III    A        Mat  55     gphss   Nan

现在，我需要通过保留其余的列值来找出基于“类”，“部分”和“子”的平均标记的最高排名。

Aggregated & Grouped Dataframe

    class  section  sub  marks  school  city   rank
0   I      A        Eng  65     jghss   salem  2
1   I      A        Mat  90     jghss   salem  1
2   III    A        Eng  80     gphss   salem  1
3   III    A        Mat  50     gphss   salem  2

Final Outcome

     class  section  sub  marks  school  city   rank
0    I      A        Mat  90     jghss   salem  1
1    III    A        Eng  80     gphss   salem  1

我尝试过，    df.groupby(['class','section','sub','school','city'])['marks'].mean()，但无法达到最终结果