Random sample/subset from vector per iteration

[JLC]

I missed the link to the post I referenced:

Understanding sample_new_levels = "uncertainty", "gaussian", and "old_levels"

The documentation for brms::extract_draws() says this about the sample_new_levels option: Indicates how to sample new levels for grouping factors specified in re_formula. This argument is only relevant if newdata is provided and allow_new_levels is set to TRUE. If "uncertainty" (default), include group-level uncertainty in the predictions based on the variation of the existing levels. If "gaussian", sample new levels from the (multivariate) normal distribution implied by the group-level standa…

I have implemented what you suggest (I think referred to to as “Gaussian” in the above post). I think sampling from the observed intercepts is what’s referred to as “uncertainty”.