From @ashander on twitter:
https://twitter.com/jaimedash/status/705050995244474368
Indeed, there’s a middle ground of source()able R files that aren’t functions. One issue that it can be non-trivial to separate the wrangling from the model fitting, and sometimes you want parts of both. I actually wrote this function yesterday because I didn’t just want the data wrangled, but wanted to overlay the model predictions from a previous analysis on a different set of data.