Expressions in lattice conditional variables

Whoops - these 2 lines should have been omitted from the program:

n <- sprintf('%s      (n%s=%g, n%s=%g)', v, nam[1],n[1], nam[2],n[2])
  vn[var == v] <- n


Frank Harrell wrote

I would like to have a lattice conditioning ( | var ) variable have
expression() as values because I want panel labels to be able to use
plotmath notation for subscripts, etc.   lattice barks at this.  Does
anyone know of a trick workaround?  An attempted example program is below.
Thanks -Frank

require(lattice)
set.seed(1)
var <- c(rep('A', 100), rep('B', 100))
trt <- sample(c('T1','T2'), 200, TRUE)
x <- c(runif(100), 10*runif(100))
y <- x + c(runif(100)/10, runif(100))
N <- tapply(x, llist(var, trt), function(x) sum(!is.na(x)))
print(N)

vn <- vector('expression', length(var))
for(v in unique(var)) {
   i <- var == v
   n <- tapply(!is.na(x[i]), trt[i], sum)
   nam <- names(n)
   w <- sprintf('paste(%s,"     (", n[%s]==%g,~~n[%s]==%g,")")',
                v, nam[1], n[1], nam[2], n[2])
   cat(w, '\n')
   vn[var == v] <- parse(text=w)
   n <- sprintf('%s      (n%s=%g, n%s=%g)', v, nam[1],n[1], nam[2],n[2])
   vn[var == v] <- n
}
trt <- factor(trt)

xyplot(as.integer(trt) ~ x | vn, panel=panel.bpplot, ylim=c(0,3),
        scale=list(y=list(at=1:2, labels=levels(trt)),
          x=list(relation='free', limits=list(c(0,1),c(0,13)))),
        ylab='Treatment', layout=c(1,2))

Error in unique.default(x) :
   unimplemented type 'expression' in 'HashTableSetup'

-----
Frank Harrell
Department of Biostatistics, Vanderbilt University
--
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