Create 2 or more columns from function's output in pandas

Question

I'm trying to create two columns for a data frame from a function that returns a tuple I have an existing dataframe named df and I'm using apply lambda to calulate 2 values based upon 2 columns of my data frame

def f(a,b):
    return a+b, a-b

df['SUM'], df['DIFF'] = apply(lambda x: f(x.COLUMN_1,x.COLUMN_2)

but I'm getting the error:

ValueError: too many values to unpack (expected 2)

My function returns a series of tuples whith the same number of rows as df

Answer 1

Try the following:

import pandas as pd

df = pd.DataFrame({'a': [0,1,2], 'b': [3,4,5]})

df[['SUM','DIFF']] = df[['a','b']].apply(lambda x: pd.Series({'SUM': x['a']+x['b'], 'DIFF': x['a']-x['b']}), axis=1)

Yields:

   a  b  SUM  DIFF
0  0  3    3    -3
1  1  4    5    -3
2  2  5    7    -3