Dear Yihui
Thanks very much for drawing my attention to knitr, which I had not heard of
before. Also thanks for pointing out the bug in Sweave, which I don't fully
understand, but I don't want to spend time and effort on understanding it. So I
hope you will find time to report the bug. I was pretty sure there was a bug
somewhere that was preventing me from doing what I wanted to do in Sweave, but
I misdiagnosed the source of the problem.
I notice you didn't use print() or cat() in your short program for knitr. Is it
the case that it's necessary to use print() or cat() with \Sexpr in Sweave, but
unnecessary in knitr?
I'll stick to Sweave for my current project, and try out knitr on my next
project. I would welcome a list of documents about knitr that I should
download, so as to make it as easy as possible to get started. I don't want to
understand the internals of knitr, but I am interested in any documents on
knitr, written by you or by others, directed at the user, rather than at
programmers of packages.
Is it convenient to use vi(m) to produce knitr source? Can vi(m) be integrated
into the knitr package? My experience with editors designed specially to work
with particular products (like the built-in editor for TeXWorks on the Mac) do
not have the power of vi(m) and emacs, and I require this power.
@Duncan: thanks for indicating the use of cat() instead of print(). However,
due to the bug in Sweave pointed out by Yihui, replacing print by cat didn't
help me.
Thanks
David
On 2 Sep 2013, at 21:11, Yihui Xie wrote:
I think Thierry meant gsub(_, _, version$platform); he just
typed too quickly. The point is to escape _ using \, but then people
are often trapped in the dreams of dreams of dreams of backslashes
like the movie Inception. And then due to a long-standing bug in
Sweave for \Sexpr{} (sorry I forgot to report to R core), you will be
so confused that you can never wake up and come back to the reality.
Dream level 1: when you need a backslash in a character string, you
need \\, which really means \; you think \\_ should be good, but
no --
Dream level 2: when you need one literal \ in a regular expression as
the replacement expression, you need \\
Combine the two levels of dreams, you end up with _. in R
really means \\, which really means \ in regular expressions.
Now you are good at the regular expression level, but Sweave comes and
bites you, and that is due to this bug in the regular expression in
Sweave Noweb syntax:
SweaveSyntaxNoweb$docexpr
[1] Sexpr\\{([^\\}]*)\\}
It should have been Sexpr\\{([^}]*)\\}, i.e. } does not need to
be escaped inside [], and \\ will be interpreted literally inside [].
In your case, Sweave sees \ in \Sexpr{}, and the regular expression
stops matching there, and is unable to see } after \, so it believes
there is no inline R expressions in your document.
BTW, knitr does not have this bug and works well in your case:
\documentclass{article}
\begin{document}
\Sexpr{sub(_, _, version$platform)}
\end{document}
Regards,
Yihui
--
Yihui Xie xieyi...@gmail.com
Web: http://yihui.name
Department of Statistics, Iowa State University
2215 Snedecor Hall, Ames, IA
On Mon, Sep 2, 2013 at 2:18 PM, David Epstein
david.epst...@warwick.ac.uk wrote:
Dear Thierry,
Your suggestion doesn't work on my version of R. Here's what I get
gsub(_, \_, print(version$platform)
Error: '\_' is an unrecognized escape in character string starting \_
print(gsub(_, \_, version$platform))
Error: '\_' is an unrecognized escape in character string starting \_
sub(_, \\_, version$platform)
[1] x86_64-apple-darwin10.8.0
Sweave does not evaluate this expression when \Sexpr is applied and a tex
error results
sub(_, \\\_, version$platform)
Error: '\_' is an unrecognized escape in character string starting \\\_
Error message from R
sub(_, _, version$platform)
[1] x86\\_64-apple-darwin10.8.0
R evaluates this. However, the above examples indicate a deficiency/possible
bug in the command sub, because sub does not seem to be able to output an
expression with a single backslash.
I tried the previous version as follows in my .Rnw document
\Sexpr{print(sub(_, _, version$platform))}
When Sweave is run, this expression is evaluated to illegal LaTeX
David.
On 2 Sep 2013, at 16:47, ONKELINX, Thierry wrote:
You have to escape the underscore
\Sexpr{gsub(_, \_, print(version$platform))}
Best regards,
Thierry
Van: r-help-boun...@r-project.org [r-help-boun...@r-project.org] namens
David Epstein [david.epst...@warwick.ac.uk]
Verzonden: maandag 2 september 2013 17:38
Aan: r-help@r-project.org
Onderwerp: [R] Sweave: printing an underscore in the output from an R
command
I am working with Sweave and would like to print out into my latex document
the result of the R command
version$platform
So what I
