I agree. Hadley Wickham (a very prolific author of important R libraries) wrote a great paper about this method using one of his libraries. I'm a Python + panda

I agree. Hadley Wickham (a very prolific author of important R libraries) wrote a great paper about this method using one of his libraries. I'm a Python + pandas user, but his paper really helped me understand the approach better: https://vita.had.co.nz/papers/plyr.pdf https://vita.had.co.nz/papers/plyr.pdf