Sum column based on another column in Pandas DataFrame

Question

I have a pandas DataFrame like this:

>>> df = pd.DataFrame({'MONTREGL':[10,10,2222,35,200,56,5555],'SINID':['aaa','aaa','aaa','bbb','bbb','ccc','ccc'],'EXTRA':[400,400,400,500,500,333,333]})
>>> df
   MONTREGL SINID EXTRA
0        10   aaa   400
1        10   aaa   400
2      2222   aaa   400
3        35   bbb   500
4       200   bbb   500
5        56   ccc   333
6      5555   ccc   333

I want to sum the column MONTREGL for each groupby SINID...

So I get 2242 for aaa and so on... ALSO I want to keep the value of column EXTRA.

This is the expected result:

   MONTREGL SINID EXTRA
0      2242   aaa   400
1       235   bbb   500
2      5611   ccc   333

Thanks for your help in advance!

Answer 1

I ended up using this script:

dff = df.groupby(["SINID","EXTRA"]).MONTREGL.sum().reset_index()

And it works in this test and production.