python - Join groupby column with a comma in a Pandas DataFrame

Question

I have a dataset like this:

>>> df = pd.DataFrame({'id_sin':['s123','s123','s124','s124'],
                       'raison':['first problem','second problem','album','dog']
    })
>>> df
  id_sin          raison
0   s123   first problem
1   s123  second problem
2   s124           album
3   s124             dog

This is the expected output:

  id_sin                         raison
0   s123  first problem, second problem
1   s124                     album, dog

What I tried:

df['raison'] = df.groupby('id_sin')['raison'].apply(lambda x: ', '.join(x))

But doesn't work... what am I missing? Thanks for help!

Answer 1

Try using agg:

df.groupby('id_sin')['raison'].agg(', '.join).reset_index()

Output:

  id_sin                         raison
0   s123  first problem, second problem
1   s124                     album, dog