Sweave with pdf(): how to remove mention "null device"

Note that the 'problem' is with dev.off(), not pdf(), and the answer 
is ?invisible.

pdf()
invisible(dev.off())

Hi

I am sorry, my question seems simple and must already have been asked, but I 
did not find any aswser on the archives :-(
Searching for the irrelevant 'pdf()' will not have helped, I fear ...
I am trying to use a plot in Sweave, where I include myself the statement
<<results=tex,echo=FALSE>>=
pdf("plot.pdf")
plot(runif(100))
dev.off()
cat("\\includegraphics{plot}\n\n")

@

as is documented in the Sweave user guide A.9. The problem is that a "null 
device 0" is printed in my document! Indeed, each time one opens pdf() or any 
device, some mention "pdf" inevitably shows up... try:

pdf()
plot(runif())
dev.off()

How can one get rid of this? The only workaround I found is to place it into 
a if() loop:

for(i in 1:1){
pdf()
plot(runif())
dev.off()
}

so there is no track of the mention null device, and my sweave pdf looks 
better. Any idea of a more elegant solution?

Thanks!!

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Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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Sweave with pdf(): how to remove mention "null device"

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