Strips at top and side for conditioned RasterStack plot

Question

For the following RasterStack, the individual layers are grouped according to two factors (upper case letters, and lower case letters).

library(raster)
s <- stack(replicate(6, raster(matrix(runif(100), 10))))
names(s) <- do.call(paste, c(expand.grid(LETTERS[1:2], letters[1:3]), sep='_'))
spplot(s)

I'd like to avoid repeating the levels' labels, ideally by having a single strip at the top with the labels A and B, and a single strip down the left or right side with labels a, b and c. Something like the following, but for a RasterStack.

library(latticeExtra)
useOuterStrips(
    xyplot(y~x|grp1+grp2, 
           data.frame(x=runif(600), y=runif(600), 
                      grp1=rep(LETTERS[1:2], each=100), 
                      grp2=rep(letters[1:3], 200)),
           strip=strip.custom(style=1), as.table=TRUE))

I'd like a lattice-based solution (including rasterVis::levelplot), since that way the plot I'm attempting to create will fit in nicely alongside other work. That said, I'm open to a ggplot2 solution.

Answer 1

I guess I was overthinking this...

library(tidyr)
cbind(as.data.frame(s), coordinates(s)) %>%
  gather(group, val, -x, -y) %>%
  separate(group, c('grp1', 'grp2'), '_') %>%
  levelplot(x=val~x+y|grp1+grp2, aspect='iso', 
            scales=list(alternating=FALSE, tck=1:0)) %>%
  useOuterStrips