How do I determine compartment number?

[billdenney]

While working on some stuff for babelmixr2, I want to know how to map from a compartment name to a compartment number. I found this vignette (https://nlmixr2.github.io/rxode2/articles/rxode2-cmt.html#changing-compartment-numbers-by-pre-declaring-the-compartments), and it suggests that there is a $state attribute. When I looked at an rxUi object, I see that ui$mvFromExpression$state is there with compartment names.

Is ui$mvFromExpression$state the best way to get a name-to-number mapping, or is there a better way?

[billdenney]

I think that I found my own answer: rxode2::rxModelVars(ui)$state

[mattfidler]

I think it may work on functions too, but am unsure.