Difference between count and nunique formatting
The count with groupby gives the number of entries while nunique gives the number of unique entries. The problem is that we get an additional column
```python
>>> df = pd.DataFrame({"A": [0,0,1,1,0], "B": [1,2,3,4,5]})
>>> df.groupby("A").count()
   B
A   
0  3
1  2
>>> df.groupby("A").nunique()
   A  B
A      
0  1  3
1  1  2
```
Why is the A column being added in nunique output?