Generate Column Name Lookup in Python

Asker: ignoring_gravity

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Disclaimer: Solution by ChatGPT and validated by human.

Question

Say I have

df = pl.DataFrame({
    'a': [1, 2, 1],
    'b': [2, 1, 2],
    'c': [3, 3, 2],
    'column': ['a', 'c', 'b'],
})

shape: (3, 4)
┌─────┬─────┬─────┬────────┐
│ a   ┆ b   ┆ c   ┆ column │
│ --- ┆ --- ┆ --- ┆ ---    │
│ i64 ┆ i64 ┆ i64 ┆ str    │
╞═════╪═════╪═════╪════════╡
│ 1   ┆ 2   ┆ 3   ┆ a      │
│ 2   ┆ 1   ┆ 3   ┆ c      │
│ 1   ┆ 2   ┆ 2   ┆ b      │
└─────┴─────┴─────┴────────┘

I want add a column which, for each row, take the value in the row corresponding to the column in column.

Expected output:

shape: (3, 5)
┌─────┬─────┬─────┬────────┬────────┐
│ a   ┆ b   ┆ c   ┆ column ┆ lookup │
│ --- ┆ --- ┆ --- ┆ ---    ┆ ---    │
│ i64 ┆ i64 ┆ i64 ┆ str    ┆ i64    │
╞═════╪═════╪═════╪════════╪════════╡
│ 1   ┆ 2   ┆ 3   ┆ a      ┆ 1      │
│ 2   ┆ 1   ┆ 3   ┆ c      ┆ 3      │
│ 1   ┆ 2   ┆ 2   ┆ b      ┆ 2      │
└─────┴─────┴─────┴────────┴────────┘

Solution

import pandas as pd

df = pd.DataFrame({
    'a': [1, 2, 1],
    'b': [2, 1, 2],
    'c': [3, 3, 2],
    'column': ['a', 'c', 'b'],
})

df['lookup'] = df.apply(lambda row: row[row['column']], axis=1)
print(df)

Reference

Lookup column name in column