I'm right there with you about R and imperative transformation and munging. Get your data scientists using sqldf...it is by far the best solution out there for this problem for R users.
I agree with using sqldf, it is a wonderful tool in R. I am sure you are aware already, but for those who are not, sqldf does not support window functions with it being based on sqlite. Just wanted to point this out as the original article emphasizes them.
Actually the sqldf R package supports 4 backend databases (sqlite, h2, postgresql, mysql), not just sqlite, and postgresql does support window functions.