Transforming data frame in python

Question

I have a situation where I have the following dataset:

ID      A     B    C
1      aa     -    -
2      -      bb   -
3      -      -    cc
4      aaa    -    -

that should be transformed to the following data frame:

ID    A
 1    aa
 2    bb
 3    cc
 4    aa

So essentially shifting rows so that it fits to the first column

Answer 1

you can use bfill with axis along columns after replace the symbol '-' by nan:

df_ = df.replace('-', np.nan).bfill(1)[['ID', 'A']]
print(df_)
  ID    A
0  1   aa
1  2   bb
2  3   cc
3  4  aaa