pandas replace part of a column with another column

Question

I have a pandas data frame, let's call it data. data has two columns, column a and column b. Like this:

  a          b
0 aaa        tts
1 abb        tst
2 aba        tss

I would like to replace each "a" in column a with column b.Like this:

  a          b
0 ttsttstts tts
1 tstbb      tst
2 tssbtss    tss

I tied something like this :

data['a'] = data['a'].apply(lambda x:x.replace("sub-string",data['b']))

but as I excepted, did not work. Could anyone please tell me what to do?

Answer 1

You need to iterate row-wise on the df (passing axis=1) so that you can access the individual 'b' column values that you intend to replace all occurrences of 'a' in the first column:

In [51]:
df['a'] = df.apply(lambda x: x['a'].replace('a',x['b']), axis=1)
df

Out[51]:
           a    b
0  ttsttstts  tts
1      tstbb  tst
2    tssbtss  tss