python dataframe: return column name in apply lambda

Question

I want to use apply(applymap) and lambda functions to get the column name for every element in dfx (a dataframe). The lambda function is used for mapping another dataframe into dfx, and it will be rewritten afterwards.

dfx

             A     B    C
2011-01-10   123   12   123 
2011-01-10   12    32   312
2011-01-11   44    1    30.99   

pseudocode

output = dfx.apply(lambda r:r.column)

I don't know how to write this part "r:r.column"

intended output

             A    B    C
2011-01-10   A    B    C 
2011-01-10   A    B    C
2011-01-11   A    B    C  

Any help is more than welcome! Thanks a lot!!

Answer 1

You can assign via pd.DataFrame.iloc:

df.iloc[:] = df.columns

print(df)

            A  B  C
2011-01-10  A  B  C
2011-01-10  A  B  C
2011-01-11  A  B  C