Stratification by 2 variables doesn't respect factor order

[timwaterhouse]

Hi Ron, thanks for the great package that I've gotten a lot of use out of. It seems that when stratifying by 2 factors, those are coerced to characters at some point because the ordering is lost (i.e., ordered alphabetically instead).

In this example, I'd expect xfac to be ordered "b, a, c" and yfac to be ordered "e, d, f". This seems to work when stratifying by only xfac, but not by both.

library(tidyverse)
library(vpc)
obs0 <- simple_data$obs
ids <- obs0 %>%
  distinct(ID) %>% 
  mutate(
    xfac = sample(letters[1:3], n(), replace = TRUE),
    xfac = factor(xfac, levels = c("b", "a", "c")),
    yfac = sample(letters[4:6], n(), replace = TRUE),
    yfac = factor(yfac, levels = c("e", "d", "f"))
  )
sim <- simple_data$sim %>% left_join(ids)
#> Joining with `by = join_by(ID)`
obs <- obs0 %>% left_join(ids)
#> Joining with `by = join_by(ID)`
vpc(sim = sim, obs = obs, stratify = "xfac") + theme_bw()

vpc(sim = sim, obs = obs, stratify = c("xfac", "yfac")) + theme_bw()

^{Created on 2024-12-11 with reprex v2.1.1}