applying several functions in transform in pandas

Question

After a groupby, when using agg, if a dict of columns:functions is passed, the functions will be applied in the corresponding columns.

Answer 1

With the updates to Pandas, you can use the assign method, along with transform to either append new columns, or replace existing columns with new values :

grouper = df_test.groupby("a")

df_test.assign(b=grouper["b"].transform("cumsum"), 
               c=grouper["c"].transform("cumprod"))

    a   b   c
0   1   2   3
1   1   22  90
2   2   30  50
3   1   24  2970
4   2   34  2500