I have a dataset that have binary values for flags for each sinid like this:

```
>>> df = pd.DataFrame({'sinid':['abc','def','ghi','abc','ghi'],'flag1':[1,1,0,0,1],'flag2':[1,0,1,0,0]})
>>> df
  sinid  flag1  flag2
0   abc      1      1
1   def      1      0
2   ghi      0      1
3   abc      0      0
4   ghi      1      0

```

I want to add values for each sinid, I think I need groupby but not sure how to use it...

This is the expected result:

```
  sinid  flag1  flag2
0   abc      1      1
1   def      1      0
2   ghi      1      1

```