Re: ob-R, problem with try/catch

[tsd@tsdye.com (Thomas S. Dye)]

Aloha Rainer,

Rainer M Krug <r.m.krug@gmail.com> writes:

>>> 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. 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.

I'm picking up a project that I last worked on in 2013.  I was under the
impression that the source code blocks were working at that time, but I
guess it is possible that I added the rm() statements after the code
blocks were working and didn't realize that the addition broke them.  I
haven't looked too deeply into the problem, but just assumed that the
session expressed in the source code block behaved as if it were entered
at the R prompt.

In the R session, I see this, which I initially thought was an error:

> png(filename="r/buck-shoulder-hist.png",width=400,height=300); tryCatch({
b <- ggplot(x, aes(x=((thickness_shoulder * 100) / mapply(max, width_shoulder_front, width_shoulder_back))))
b + geom_histogram(aes(y=..density..))  + geom_density(weight=2) +
xlab("Buck's Shoulder Index") + facet_wrap(~ turner)
rm(b)
},error=function(e){plot(x=-1:1, y=-1:1, type='n', xlab='', ylab='', axes=FALSE); text(x=0, y=0, labels=e$message, col='red'); paste('ERROR', e$message, sep=' : ')}); dev.off()
'org_babel_R_eoe'
+ . + null device 
          1 

hth,
Tom

-- 
Thomas S. Dye
http://www.tsdye.com