[R] Sweave question: prevent expansion of unevaluated reused code chunk

[Duncan Murdoch]

On 3/13/2007 7:02 PM, Kevin R. Coombes wrote:
> Hi,
> 
> Consider the following (much simplified) Sweave example:
> 
> --------------
> 
> First, we set the value of $x$:
> <<chunk1,eval=FALSE>>=
> x <- 1
> @
> 
> Then we set the value of $y$:
> <<chunk2,eval=FALSE>>=
> y <- 2
> @
> 
> Thus, the overall algorithm has this structure:
> <<combined,eval=FALSE>>=
> <<chunk1>>
> <<chunk2>>
> @
> 
> <<justDoIt,echo=FALSE>>=
> <<combined>>
> @
> 
> ---------------
> 
> I'd like to be able to do something like this, where the "combined" 
> chunk prints out in the final LaTeX document essentially verbatim.  In 
> particular, I want to see the "<<chunk1>>" unexpanded in that block, 
> since this gives me a nice conceptual overview of the algorithm. (Of 
> courser, this is more useful when chunk1 and chunk2 are much longer than 
> they are in this example....)
> 
> Is there an option that allows me to get this behavior?

As others have said, the answer is currently no, but in R 2.5.0 this 
should be a relatively easy modification (because it has the ability to 
echo your input, rather than a deparsed version of it).  In the other 
platforms you've used, is there a standard syntax to indicate whether or 
not you want the chunks expanded?  I can see either behaviour as being 
desirable in different circumstances.  Sometimes you want the reader to 
know about your chunk names, and sometimes you don't.

Duncan Murdoch