What is correct syntax to swap column values for selected rows in a pandas data frame using just one line?

Question

I am using pandas version 0.14.1 with Python 2.7.5, and I have a data frame with three columns, e.g.:

import pandas as pd

d = {\'L\':  [\'left\', \'right\',         


        

Answer 1

You can also do this with np.select and df.where i.e

Option 1: np.select

df[['L','R']] = pd.np.select(df['VALUE'] == 1, df[['R','L']].values, df[['L','R']].values)

Option 2: df.where

df[['L','R']] = df[['R','L']].where(df['VALUE'] == 1, df[['L','R']].values)

Option 3: df.mask

df[['L','R']] = df[['L','R']].mask( df['VALUE'] == 1, df[['R','L']].values)

Output:

    L      R  VALUE
0  left  right     -1
1  left  right      1
2  left  right     -1
3  left  right      1
4  left  right     -1
5  left  right      1