create new column of incremental number based on 2 categorical columns pandas dataframe

Question

I have a pandas dataframe with the columns username and phase . I want to create a separate column called count with incremental values.

The count will be based on how many times a username has appeared in a specific phase . How can I accomplish this efficiently? Any suggestion is appreciated.

    username  phase      count
0    andrew    1          1
1    andrew    1          2
2    alex      1          1
3    alex      2          1
4    andrew    1          3
5    cindy     3          1
6    alex      2          2

Answer 1

You can use cumcount after groupby on username and phase .

df['count'] = df.groupby(['username', 'phase']).cumcount()+1
print(df)

---

  username  phase  count
0   andrew      1      1
1   andrew      1      2
2     alex      1      1
3     alex      2      1
4   andrew      1      3
5    cindy      3      1
6     alex      2      2