R Under development (unstable) (2024-01-23 r85822 ucrt) -- "Unsuffered Consequences"
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> library(directlabels)
> if(require(lattice) && require(nlme)){
+   data(BodyWeight, package="nlme")
+   oldopt <- lattice.options(panel.error=NULL)
+   p <- xyplot(weight~Time|Diet,BodyWeight,groups=Rat,type='l',
+               layout=c(3,1),xlim=c(-10,75))
+   stop.if.same.colour <- function(d, ...){
+     col.tab <- table(d$colour)
+     if(1 == length(col.tab)){
+       print(d)
+       stop("only one colour")
+     }
+     d
+   }
+   dl <- direct.label(p, list("angled.boxes", "stop.if.same.colour"))
+   print(dl)
+   lattice.options(oldopt)
+ }
Loading required package: lattice
Loading required package: nlme

Attaching package: 'nlme'

The following object is masked from 'package:directlabels':

    gapply

> 
> proc.time()
   user  system elapsed 
   0.53    0.12    0.64