[R] knitr and stopifnot replacement.

[Bart Kastermans]

On 22 Aug 2014, at 12:39, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:

> On 22/08/2014, 6:02 AM, Bart Kastermans wrote:
>> I have a daily generated report in which I put a check using stopifnot.  Unfortunately
>> I didn’t check the effect very well, turns out that if the condition checked fails
>> this is not shown in the knitr output (I only get an error much later due to a missing
>> object).
>> 
>> So my question is, what is the correct way to use assertions in a <filename>.Rnw
>> file.  I want to perform a check, and if it fails everything should stop with a message
>> I can generate.
>> 
> 
> One of the differences between knitr and Sweave is that knitr handles
> errors, and Sweave doesn't.  I expect there's some knitr option to tell
> it to quit in case of error (a hook?), but you'll have to check the
> documentation to find it.

Thanks; that helped me to find the exact right option:

<<filelist, error=FALSE>>=
# check all files exist before continuing
stopifnot(all(sapply(files, file.exists)))
@


> 
> Duncan Murdoch
>