pandas dataframe columns to a single cell

Question

I have the dataframe:

df = A B l1 l2 l3
     1 1 2   3  4
     1 1 3   5  7
     1 1 1   2  9
     1 2 2   7  8

I want to groupby A,B, per columns, and put the values as a series in a cell. So the output will be:

df = A B   l1      l2    l3
     1 1  2,3,1  3,5,2  4,7,9
     1 2   2       7      8

How can I do it? (efficiently)

Also, What is the solution of no ID columns? so

df = l1 l2 l3
     2   3  4
     3   5  7
     1   2  9
     2   7  8

and the output:

df =  l1      l2    l3
     2,3,1,2  3,5,2,7  4,7,9,8

Answer 1

Use GroupBy.agg with lambda function with cast to strings and join :

df1 = df.groupby(['A','B']).agg(lambda x: ','.join(x.astype(str))).reset_index()
print (df1)
   A  B     l1     l2     l3
0  1  1  2,3,1  3,5,2  4,7,9
1  1  2      2      7      8

For second:

df2 = df.astype(str).agg(','.join).to_frame().T
print (df2)
        l1       l2       l3
0  2,3,1,2  3,5,2,7  4,7,9,8

If there are strings:

df1 = df.groupby(['A','B']).agg(','.join).reset_index()
df2 = df.agg(','.join).to_frame().T