[R] Finding the first value without warning in a loop

[Gabor Grothendieck]

log(-1) is not an error in R bug it does generate a warning and a NaN result.

If there is a warning then the statement that causes the warning and all
remaining statements in the tryCatch are not executed.  Instead the
warning= function is invoked.

On Sun, Dec 7, 2008 at 1:09 PM, David Winsemius <dwinsemius at comcast.net> wrote:
> Thanks for that. I am having some difficulty figuring out how it works. The
> help page tells me (I think) that "y<-log(x)" gets matched to expr. Am I
> correct in thinking that if either an error or warning is produced, that
> tryCatch silently returns <something>  (or <nothing>?) to the for loop, and
>  only otherwise goes on to evaluate the rest of the second assignment and
> break call? So any warning would abort processing of the remaining
> expressions?
>
> Are the assignment "xx<-x" and the break call considered "handlers" as
> described in the help page?
>
> I see the purpose of the last argument. Taking out the warning =
> function(w{}) changes the behavior when none of the elements in the vector
> passed to x were valid.
>
>> for (x in c(-2, -1)) {
> +       tryCatch({
> +               y <- log(x)
> +               xx <- x
> +               break
> +       })
> + }
> Warning message:
> In log(x) : NaNs produced
>> print(xx)
> [1] -2
>
>
> --
>
> David Winsemius
>
> On Dec 7, 2008, at 12:21 PM, Gabor Grothendieck wrote:
>
>> Try this:
>>
>> for (x in c(-2, 2, 4)) {
>>        tryCatch({
>>                y <- log(x)
>>                xx <- x
>>                break
>>        }, warning = function(w) {})
>> }
>> print(xx) # 2
>>
>>
>>
>> On Sun, Dec 7, 2008 at 2:38 AM, Andreas Wittmann
>> <andreas_wittmann at gmx.de> wrote:
>>>
>>> Dear R useRs,
>>>
>>> with the following piece of code i try to find the first value which can
>>> be
>>> calculated without warnings
>>>
>>> `test` <- function(a)
>>> {
>>> repeat
>>> {
>>>  ## hide warnings
>>>  suppressWarnings(log(a))
>>>
>>>  if (exists("last.warning", envir = .GlobalEnv))
>>>  {
>>>   a <- a + 0.1
>>>   ## clear existing warnings
>>>   rm("last.warning", envir = .GlobalEnv)
>>>  }
>>>
>>> if(a > 5 || !exists("last.warning", envir = .GlobalEnv))
>>>  break
>>> }
>>>
>>> return(a)
>>> }
>>>
>>> if i run this with test(-3), i would expect a=0 as return value.
>>> Is it also possible to hide warnings during my function, i guess i use
>>> suppressWarnings in a wrong way here?
>>>
>>> Thanks and best regards
>>>
>>> Andreas
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>