[R] Lattice in a loop does not produce output

[Alex van der Spek]

I cannot understand why xyplot does not work within a simple for loop.

This works up to the for loop; inside the for loop the png files are
opened and closed, but nothing is plotted. No error messages are written
to the console either. This is the case on both Windows and Linux. 

By the way, running the script below on Linux using source() does not
even produce the first xyplot. This is less of an issue for me though. 

#! usr/bin/env R
# Test lattice loop

rm(list=ls())

x<-1:16
y<-2*x-1
z<-rep(c('A','B','C','D'),4)

xyz<-data.frame(x=x,y=y,z=z)

require(lattice)

png('Test.png')
xyplot(y~x|z)
dev.off()

for (i in 1:5) {
f<-paste('Test',i,'.png',sep='')
png(f)
xyplot(y~x|z)
dev.off()
}