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)})


        

Answer 1

the following solution to this frustratingly frustrating question works for me. I found the original suggestion in another StackOverflow post a while ago. The trick is to wrap up the return values into a Series like this:

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

Then this works as you wanted:

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

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

Answer 3

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

Should do the trick.

(I show this example so you can see how to use multiple columns as the input to create multiple new columns)

Answer 4

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)))