Re: ob-R, problem with try/catch

["Charles C. Berry" <ccberry@ucsd.edu>]

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On Wed, 22 Apr 2015, Rainer M Krug wrote:

>
>
> Envoyé de mon iPhone
>
>> Le 23 avr. 2015 à 04:23, Charles C. Berry <ccberry@ucsd.edu> a écrit :
>>
>>> On Wed, 22 Apr 2015, Thomas S. Dye wrote:
>>>
>>> Aloha all,
>>>
>>> Prior to eaa3a761dae, when working in a session, I was able to run this
>>> R source code block without problems:
>>>
>>> ,-----------------------------------------
>>> | #+header: :file r/adze_wt_log.pdf
>>> | #+header: :results output graphics
>>> | #+header: :width 4 :height 3
>>> | #+begin_src R
>>> |   g <- ggplot(x, aes(x = weight))
>>> |   g + geom_histogram(aes(y=..density..))
>>
>> ## Try this:
>>
>> print( g + geom_histogram(aes(y=..density..)) ) # before rm(g).
>>
>>
>>> |   rm(g)
>>> | #+end_src
>>> `-----------------------------------------
>>>
>>> After eaa3a761dae, I get an error and an empty output file.
>>
>> That commit introduced a tryCatch() wrapper for graphics results.
>>
>> You probably know that ggplot (or ggplot2) relies on printing of objects to produce graphics (see R-FAQ 7.22).
>>
>> tryCatch(expr,...) evaluates expr and returns its value, which is `rm(g)' in your case. But `rm(g)' is not autoprinted, and you get an empty file.
>
> I am not in front of my computer but there must be more, as even before 
> the commit there should have been empty file for exactly the same 
> reason.

`:results output' will return the autoprinted values. Without tryCatch it 
works.


> Also, the error is strange. Could you send a small reproducable example, 
> so that we can see which error you get? Because if you get an error and 
> an empty file, an error must be in the tryCatcb block.

Here are two blocks that differ in using tryCatch. The first produces an 
empty, malformed pdf. The second produces a valid pdf. If you comment out 
the `invisible()' line in the first, then both will produce similar valid 
pdf's.

#+header: :file nada.pdf
#+header: :results output graphics
#+header: :width 4 :height 3
#+begin_src R
   require(ggplot2)
   df <-
       data.frame(gp = factor(rep(letters[1:3], each = 10)),
                  y = rnorm(30))
   ggplot(df, aes(x = gp, y = y)) + geom_point()
   invisible()
#+end_src


#+BEGIN_SRC R :results output
   require(ggplot2)
   pdf(file="aok.pdf",width=4,height=3)
   df <-
       data.frame(gp = factor(rep(letters[1:3], each = 10)),
                  y = rnorm(30))
   ggplot(df, aes(x = gp, y = y)) + geom_point()
   invisible()
   dev.off()
#+END_SRC



HTH,

Chuck