How does Sweave write to a file?

Hello.

I need that Sweave writes R output to a file. To do it, I put the following into the foo.Rnw file:


\documentclass{article}
\usepackage{Sweave}
\begin{document}

...

<<echo=F>>=
x<- rnorm(100)
y<- rnorm(100)
sink("foo.txt")
summary(lm(y~x))
sink()
@

...

\end{document}


When I run:

R CMD Sweave foo.Rnw

R responses:

Warning message:
In sink() : no sink to remove,

and It doesn't work. Somebody knows how I can fix it?

The problem is that Sweave executes each statement wrapped within sink( 
con ); statement; sink().  You need to avoid using sink() as a separate 
statement.  One way would be to put the lines

sink("foo.txt")
summary(lm(y~x))
sink()

into a block using braces {}; Sweave would wrap the whole function call, not the individual lines.  That's essentially what
capture.output() does, so this should work:

writeLines( capture.output( summary(lm(y~x)) ), "foo.txt")

You can probably do it in other ways too.

Duncan Murdoch