How to assign two values to two columns using one lambda sentence in pandas

I’ve got a function which returns two values like:

def myfunc(x):
   return a, b

And I want to assign a and b to two columns in my dataset, currently I use code like:

df.loc[:,'col1'] = df['col0'].apply(lambda x: myfunc(x)[0])
df.loc[:,'col2'] = df['col0'].apply(lambda x: myfunc(x)[1])

Certainly it’s inefficient because it calls myfunc twice. But I don’t know how to assign values to two columns using one sentence in this circumstance. Can anyone give some help pleaseeeee?

>Solution :

You should convert the function output to Series:

def myfunc(x):
    # dummy example
    return x+1, x**2

df = pd.DataFrame({'col': [1,2,3,4]})
df[['col2', 'col3']] = df['col'].apply(lambda x: pd.Series(myfunc(x)))

NB. this kind of operation is slow, better find a way to make your function vectorial

output:

   col  col2  col3
0    1     2     1
1    2     3     4
2    3     4     9
3    4     5    16

Alternatively, this might be slightly more efficient as the dataframe constructor is called only once (vs one Series per row above):

df[['col2', 'col3']] = pd.DataFrame(zip(*df['col'].apply(myfunc))).T