Use better example in pd.lookup replacement

[MarcoGorelli]

#39171 (comment)

In the user guide, let's use

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

instead of the current workaround

https://pandas.pydata.org/pandas-docs/dev/user_guide/indexing.html#looking-up-values-by-index-column-labels

cc @erfannariman
also cc @quanghm in case you have further comments on this

[raghuabhishek]

Hi MacroGorelli, Can I take this issue and work on it.

[MarcoGorelli]

sure, PRs welcome

[raghuabhishek]

Thanks MarcoGorelli, I have raised a PR #42110. Can you pls review it and let me know if there are changes required.