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

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?

CodePudding user response：

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