這個問題在這里已經有了答案：
![如何在不合并的情況下按列將組附加到主資料框？[復制]](https://img.uj5u.com/2022/02/18/b9505b66156745138fe5291cee99a0ad.png)
uj5u.com熱心網友回復：
采用：
df['backlog_wish_req_mean_days']=(df.groupby(['stud_id','sub_code'])['backlog_wish_req_diff']
.transform('mean'))
print (df)
stud_id sub_code ques_date resp_date marks next_ques_date \
3 101 CSE01 2016-03-27 29/03/2016 90 2017-11-11
2 101 CSE01 2017-11-11 14/11/2017 55 2018-01-10
1 101 CSE01 2018-01-10 11/1/2018 86 2020-11-13
0 101 CSE01 2020-11-13 NaN 77 NaT
7 101 CSE02 2006-02-27 28/02/2006 67 2007-01-11
6 101 CSE02 2007-01-11 NaN 80 2008-11-10
5 101 CSE02 2008-11-10 NaN 90 2010-05-13
4 101 CSE02 2010-05-13 NaN 65 NaT
backlog_wish_req_diff backlog_wish_req_mean_days
3 594.0 564.0
2 60.0 564.0
1 1038.0 564.0
0 NaN 564.0
7 318.0 512.0
6 669.0 512.0
5 549.0 512.0
4 NaN 512.0
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標籤：Python 熊猫 数据框 麻木的 熊猫-groupby