grouping pandas dataframe by two columns (or more)?

Question

I have the following dataframe:

mydf = pandas.DataFrame({\"cat\": [\"first\", \"first\", \"first\", \"second\", \"second\", \"third\"], \"class\": [\"A\", \"A\",         


        

Answer 1

Use reset_index

In [9]: mydf.groupby(['cat', "class"]).val.sum().reset_index()
Out[9]: 
      cat class  val
0   first     A    7
1  second     B    3
2   third     C   10

EDIT

set level=1 if you want to set cat as index

In [10]: mydf.groupby(['cat', "class"]).val.sum().reset_index(level=1)
Out[10]: 
       class  val
cat              
first      A    7
second     B    3
third      C   10

You can also set as_index=False to get the same output

In [29]: mydf.groupby(['cat', "class"], as_index=False).val.sum()
Out[29]: 
      cat class  val
0   first     A    7
1  second     B    3
2   third     C   10