Dataframe Apply method to return multiple elements (series)

Question

import pandas as pd

Let's say I have a dataframe like so:

df = pd.DataFrame({"a":range(4),"b":range(1,5)})

it looks like this:

   a  b
0  0  1
1  1  2
2  2  3
3  3  4

and a function that multiplies X by Y:

def XtimesY(x,y):
    return x*y

If I want to add a new pandas series to df I can do:

df["c"] =df.apply( lambda x:XtimesY(x["a"],2), axis =1)

It works !

Now I want to add multiple series:

I have this function:

def divideAndMultiply(x,y):
    return x/y, x*y

something like this ?:

df["e"], df["f"] = df.apply( lambda x: divideAndMultiply(x["a"],2) , axis =1)

It doesn't work !

I want the 'e' column to receive the divisions and 'f' column the multiplications !

Note: This is not the code I'm using but I'm expecting the same behavior.

Answer 1

Almost there. Use zip* to unpack the function. Try this:

def divideAndMultiply(x,y):
    return x/y, x*y

df["e"], df["f"] = zip(*df.a.apply(lambda val: divideAndMultiply(val,2)))

Answer 2

UPDATE

Updated for version 0.23 - using result_type='broadcast' for further details refer to documentation

Redefine your function like this:

def divideAndMultiply(x,y):
    return [x/y, x*y]

Then do this:

df[['e','f']] = df.apply(lambda x: divideAndMultiply(x["a"], 2), axis=1, result_type='broadcast')

You shall get the desired result:

In [118]: df
Out[118]:
   a  b  e  f
0  0  1  0  0
1  1  2  0  2
2  2  3  1  4
3  3  4  1  6