cannot create postscript files with trellis graphics inside a function

Dear Faheem,

If I define

foo <-function()
{
  x <- rnorm(500)
  trellis.device(postscript, file="plot.ps")
  densityplot(~x)
  dev.off()
 }

and call foo() then plot.ps is just a blank plot. However, if I extract
the lines inside foo and run them, ie.

x <- rnorm(500)
trellis.device(postscript, file="plot.ps")
densityplot(~x)
dev.off()

then plot.ps is created without problems. The former method worked with
the regular postscript() device, which I used to use all the time inside
functions.

I've never used lattice/trellis graphics before. Is this a bug or am I
doing something wrong?

Lattice-graphics functions return objects rather than drawing plots as side 
effects. When you call a lattice function such as densityplot directly at 
the command plot, print is invoked implicitly and "prints" the plot. Within 
a function, you have to call print explicitly -- e.g., print(densityplot(~x)).

I hope that this helps,
  John
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
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