Hello I’m having troubles dealing with Pandas. I’m trying to sum duplicated rows on a multiindex Dataframe.

I tryed with `df.groupby(level=[0,1]).sum()`

, also with `df.stack().reset_index().groupby(['year', 'product']).sum()`

and some others, but I cannot get it to work.

I’d also like to add every unique product for each given year and give them a 0 value if they weren’t listed.

Example: dataframe with multi-index and 3 different products (A,B,C):

```
volume1 volume2
year product
2010 A 10 12
A 7 3
B 7 7
2011 A 10 10
B 7 6
C 5 5
```

Expected output : if there are duplicated products for a given year then we sum them.

If one of the products isnt listed for a year, we create a new row full of 0.

```
volume1 volume2
year product
2010 A 17 15
B 7 7
C 0 0
2011 A 10 10
B 7 6
C 5 5
```

Any idea ? Thanks