使用GroupBy向数据框添加新列

Question

I have a data frame like so

id val1 val2
0   A    B
1   C    D
1   E    F
2   G    H

and trying to reshape into...

id val1 val2 val3 val4
0   A    B
1   C    D    E    F
2   G    H

It doesn't matter what the additional column names are and I may not know how many duplicates there are of each id, so I may not know exactly how many columns to add.

Any advice for solving a problem like this? I've been trying to use pandas and groupBy, but I'm not constrained to either. Thanks!

Answer 1

This is a pivot problem, but you'll need to convert your frame from wide to long before you can pivot it:

u = df.melt('id')
u.assign(variable=u.groupby('id').cumcount()).pivot(*u)

variable  0  1    2    3
id                      
0         A  B  NaN  NaN
1         C  E    D    F
2         G  H  NaN  NaN