Is there an equivalent of make_standata from brms for rstanarm? If not, does anyone have a suggested workflow or example for pre-processing inputs to rstanarm generated stan models?

I can always just re-express the model in brms and go from there fairly easily, just seems feasible that perhaps something similar exists for rstanarm that I could leverage. I wasn’t able to find anything after searching the forum a bit and googling, so asking.

There’s not really an equivalent unfortunately. The closest would be running stan_glm.fit() with chains=0. That returns the list of data but stan_glm.fit() takes its input as a design matrix and not a formula so that could be annoying to work with (it’s mainly intended for internal use so this behavior with chains=0 isn’t documented).