Re: Using cat() with R prints R session prompt (>) in results block

[John Hendy <jw.hendy@gmail.com>]

On Sat, Mar 23, 2013 at 5:20 PM, Eric Schulte <schulte.eric@gmail.com> wrote:
> [...]
>> I'm getting the > prompt from my R session output
>> with the cat() command. For example:
>>
>> #+name: test
>> #+begin_src R :session r :results output raw :exports results
>>
>> cat(paste("#+end_center"))
>> cat("\n")
>>
>> #+end_src
>>
>> #+RESULTS: test
>> #+end_center>
>>
>> How do I stop that?
>>
>> As a side note... if I remove cat("\n"), nothing gets put into the
>> #+results block -- it's just empty. I don't understand why.
>>
>
> Hi John,
>
> This seems to be related to newlines and the parsing of session output.
> Results aren't noticed without a newline, and when intermediately
> printed results do not end in a newline, the prompt is pasted along with
> the results.
>
> If we look at the R session buffer, the cause of this bad behavior can
> be seen.
>
>     ,----[ESS buffer]
>     | > cat(paste("#+end_center"))
>     | cat("\n")
>     | 'org_babel_R_eoe'
>     | cat(paste("#+end_center"))
>     | #+end_center> cat("\n")
>     |
>     |
>     | > 'org_babel_R_eoe'
>     | [1] "org_babel_R_eoe"
>     `----
>
> I'm not sure that we can (robustly and reasonably) distinguish the R
> prompt from R process output when the prompt does not appear at the
> start of a line.  Perhaps ESS could mark R prompts with a special text
> property which would make this much easier from the Org-mode side?
>

So babel filters out the ">" prompt if it's the first character? Makes sense?

> Is it possible simply to ensure that code block output lines end in
> newlines?

As in, instead of =cat(paste("#+end_center"))= use
=cat(paste("#+end_center \n"))= ?

If so, absolutely. I think for some reason I had trouble with this
once before, but I don't recall specifics. I'll give it a try on
Monday and confirm this works. If so, perhaps I could add a tidbit in
ob-R-doc about doing this when not simply including a single file for
export output.


Thanks for chiming in,
John

>
> Cheers,
>
> --
> Eric Schulte
> http://cs.unm.edu/~eschulte