How To Get Values By Row Based On Column Name in Python

We have provided an example of how to select a column using the column value as column name in R. Let’s do it also in Python:

import pandas as pd
import numpy as np
df = pd.DataFrame.from_dict({"V1": [66, 57, 79,75], "V2": [41,85,94,71], 
                             "V3":[19,3,38,58], "Selection":['V1','V3', 'V2','V3']})

df

   V1  V2  V3 Selection
0  66  41  19        V1
1  57  85   3        V3
2  79  94  38        V2
3  75  71  58        V3

We want to get a new column according to the Selection column, where the first value will be the corresponding value of V1 column the second value will be the corresponding value of V3 column and so on.

Using the lookup function

df['Value'] = df.lookup(df.index, df.Selection)
df

   V1  V2  V3 Selection  Value
0  66  41  19        V1     66
1  57  85   3        V3      3
2  79  94  38        V2     94
3  75  71  58        V3     58

Using the factorize function

idx, cols = pd.factorize(df['Selection'])
df['Value'] = df.reindex(cols, axis=1).to_numpy()[np.arange(len(df)), idx]
df

   V1  V2  V3 Selection  Value
0  66  41  19        V1     66
1  57  85   3        V3      3
2  79  94  38        V2     94
3  75  71  58        V3     58