python - Numpy vectorize alternative to get rid of Pandas Apply

Question

I am looking to pass a pandas dataframe to a custom function as efficiently as possible.

The biggest gains in speed are through vectorization and from getting rid of the overhead used by pd.apply.

It seems to me that some custom functions don't really lend themselves to vectorization (for example if the custom function contains a for loop in it.) Does this sound right?

Can someone help set the columns of a dataframe to the outputs of a function using this notation:

df['newA'], df['newB'], df['newC']= test(df.A, df.B, df.C)

The alternative options below produce results but I can't find an efficient way to input those results into the dataframe like the above would.

import numpy as np
import pandas as pd

df=pd.DataFrame(np.arange(10*3).reshape((10, 3)), columns=['A','B','C'])

def test(x,y,z):
    if x>=30:
        pass
    return x,y,z


#Option 1
vectest=np.vectorize(test, otypes=[np.ndarray])
result=vectest(df.A, df.B, df.C)


#Option 2
result=list(map(test,df.A, df.B, df.C))

All of this is to avoid a crude loop or using apply.

question from:https://stackoverflow.com/questions/65838896/numpy-vectorize-alternative-to-get-rid-of-pandas-apply

Answer 1

Waitting for answers