I have a data frame that looks like this:

```
CP   AID   type
1    1      b
1    2      b
1    3      a
2    4      a
2    4      b
3    5      b
3    6      a
3    7      b

```

I would like to groupby the CP column and filter so it only returns rows where the CP has at least 3 unique 'pairs' from the AID column. 

The result should look like this:

```
CP   AID   type
1    1      b
1    2      b
1    3      a
3    5      b
3    6      a
3    7      b

```