DataFrame: add column with the size of a group

Question

I have the following dataframe:

    fsq digits  digits_type
0    1   1       odd
1    2   1       odd
2    3   1       odd
3    11  2       even
4    22  2           


        

Answer 1

In [395]: df['count'] = df.groupby('digits')['fsq'].transform(len)

In [396]: df
Out[396]: 
   fsq  digits digits_type  count
0    1       1         odd      3
1    2       1         odd      3
2    3       1         odd      3
3   11       2        even      2
4   22       2        even      2
5  101       3         odd      2
6  111       3         odd      2

[7 rows x 4 columns]