Concatenating column values into one column in Python

Question

I have a dataframe like this (group by Col1,col2 and sort on col4,

df = Col1 col2 col3 col4
1.      A    B    1    5
2.      A    B    1    6
3.      X    Y    2    1
4.      X    Y    3    2

What I want is something like this

col1  col2 col3 col4
A      B   [1,1] [5,6]
X      Y   [2,3]  [1,2]

but unable to concatenate the col3.

I am able to do groupby and sort by col1,col2.

df =df.groupby(['col1','col2']).apply(lambda x: x.sort_values('col4'))

Answer 1

Since you said you already sorted, you only need groupby and agg with list

df.groupby(['col1','col2']).agg(list).reset_index()

Out[92]:
  col1 col2    col3    col4
0    A    B  [1, 1]  [5, 6]
1    X    Y  [2, 3]  [1, 2]