How to enumerate groups within groups in pandas

Question

I have a DataFrame like this:

      name visit foo
0   andrew    BL   a
1   andrew    BL   a
2   andrew    BL   b
3   andrew    BL   b
4      bob    BL   c
5      bob    BL   c
6      bob    BL   d
7      bob    BL   d
8      bob   M12   e
9      bob   M12   e
10     bob   M12   f
11     bob   M12   g
12   carol    BL   h
13   carol    BL   i
14   carol    BL   j
15   carol    BL   k

How can I create a new column which enumerates groups of foo per group of ['name', 'visit'], like this?

      name visit foo  enum
0   andrew    BL   a     1
1   andrew    BL   a     1
2   andrew    BL   b     2
3   andrew    BL   b     2
4      bob    BL   c     1
5      bob    BL   c     1
6      bob    BL   d     2
7      bob    BL   d     2
8      bob   M12   e     1
9      bob   M12   e     1
10     bob   M12   f     2
11     bob   M12   g     3
12   carol    BL   h     1
13   carol    BL   i     2
14   carol    BL   j     3
15   carol    BL   k     4

Answer 1

Use groupby with factorize:

df['enum'] = df.groupby(['name', 'visit'])['foo'].transform(lambda x: pd.factorize(x)[0] + 1)
print (df)
      name visit foo  enum
0   andrew    BL   a     1
1   andrew    BL   a     1
2   andrew    BL   b     2
3   andrew    BL   b     2
4      bob    BL   c     1
5      bob    BL   c     1
6      bob    BL   d     2
7      bob    BL   d     2
8      bob   M12   e     1
9      bob   M12   e     1
10     bob   M12   f     2
11     bob   M12   g     3
12   carol    BL   h     1
13   carol    BL   i     2
14   carol    BL   j     3
15   carol    BL   k     4

Answer 2

You can modify coldspeed's comment to use:

df = pd.concat([
        df,
        df.groupby([df.name, df.visit]).apply(lambda g: g.groupby('foo').ngroup() + 1).reset_index().rename(columns={0: 'enum'})['enum']],
    axis=1)
>>> df
    name    visit   foo enum
0   andrew  BL  a   1
1   andrew  BL  a   1
2   andrew  BL  b   2
3   andrew  BL  b   2
4   bob     BL  c   1
5   bob     BL  c   1
6   bob     BL  d   2
7   bob     BL  d   2
8   bob     M12 e   1
9   bob     M12 e   1
10  bob     M12 f   2
11  bob     M12 g   3
12  carol   BL  h   1
13  carol   BL  i   2
14  carol   BL  j   3
15  carol   BL  k   4