I am trying to join two pandas dataframes using two columns: new_df = pd.merge(A_df, B_df, how='left', left_on='[A_c1,c2]', right_on = '[B_c1,c2]') but got the following error: pandas/index.pyx in...

When you merge two indexed dataframes on certain values using 'outer' merge, python/pandas automatically adds Null (NaN) values to the fields it could not match on. This is normal behaviour, but it...