Join groupby column with a comma in a Pandas DataFrame

问题

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!

回答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

回答2:

Try changing the groups to lists:

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

After testing your code, it turns out that you should not do df['raison'] =... because df.groupby('id_sin')['raison'].apply(lambda x: ', '.join(x)) has length 2 with different index than df, which has length 4.

来源：https://stackoverflow.com/questions/55697144/join-groupby-column-with-a-comma-in-a-pandas-dataframe