Removing per-panel unused factors in a bar chart with nested factors

Question

Some time ago I asked a question on how to remove unused factors in a bar chart, and I got a useful solution for that problem, thanks to @Aaron. Now, I am facing a very simi

Answer 1

To do this, you'll need to supply both a modified prepanel function (which sets up the limits of each panel's plotting area) and a modified panel function (which is responsible for plotting the data). In both cases, the key modification is to use x[, drop=TRUE] to drop the unused levels:

library(lattice)

barchart(VALUE ~ BENCH | EXEC.CFG + CLASS.CFG, df, groups = METRIC,
         scales = list(x = list(rot = 45, relation = 'free')),
         prepanel = function(x,y,...) {
             xx <- x[, drop = TRUE]
             list(xlim = levels(xx),
                  xat=sort(unique(as.numeric(xx))))
         },
         panel = function(x,y,...) {
             xx <- x[, drop = TRUE]
             panel.barchart(xx, y, ...)
         },
         auto.key = list(columns = 2))