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

[Duncan Murdoch]

On 3/14/2007 11:39 AM, Kevin R. Coombes wrote:
> Hi,
> 
> I don't know of a standard way to indicate this; I would have suggested
> 
> <<combined,expand=FALSE>>
> 
> (with expand=TRUE the default), except for the fact that Seth Falcon 
> already suggested the same notation in his response...so I can only 
> second the motion.

This is now in R-devel, to become R 2.5.0 next month.

Duncan Murdoch

> 
> 	Kevin
> 
> Duncan Murdoch wrote:
>> 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
> 
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