[Rd] capturing multiple warnings in tryCatch()

[Rui Barradas]

Hello,

I remembered having seen a function tryCatch.W.E and after an online 
search, found where.
It was in a R-Help post and in demo(error.catching). The question by 
Marius Hofert [1] was answered, among others, by Martin Maechler [2] 
which included the function tryCatch.W.E.

These posts refer to an old thread dated 2004 [3], with an answer by 
Luke Tierney [4]. The function withWarnings posted by Luke returns all 
warning messages in a list, as seen below.
I repost the function to have this self contained.



withWarnings <- function (expr) {
   warnings <- character()
   retval <- withCallingHandlers(expr, warning = function(ex) {
     warnings <<- c(warnings, conditionMessage(ex))
     invokeRestart("muffleWarning")
   })
   list(Value = retval, Warnings = warnings)
}
withWarnings(foo())
#$Value
#[1] "warning 2"
#
#$Warnings
#[1] "warning 1" "warning 2"



Function tryCatch.W.E is now part of contributed package simsalapar [5], 
with credits to Marius and Martin given in its documentation.


[1] https://stat.ethz.ch/pipermail/r-help/2010-December/262185.html
[2] https://stat.ethz.ch/pipermail/r-help/2010-December/262626.html
[3] https://stat.ethz.ch/pipermail/r-help/2004-June/052092.html
[4] https://stat.ethz.ch/pipermail/r-help/2004-June/052132.html
[5] https://CRAN.R-project.org/package=simsalapar


Hope this helps,

Rui Barradas



Às 22:37 de 02/12/21, Fox, John escreveu:
> Dear Henrik, Simon, and Adrian,
> 
> As it turns out Adrian's admisc::tryCatchWEM() *almost* does what I want, which is both to capture all messages and the result of the expression (rather than the visible representation of the result). I was easily able to modify tryCatchWEM() to return the result.
> 
> Henrik: I was aware that tryCatch() doesn't return the final result of the expression, and I was previously re-executing the expression to capture the reult, but only getting the first warning message, along with the result.
> 
> Thanks for responding to my question and providing viable solutions,
>   John
> 
> On 2021-12-02, 5:19 PM, "Henrik Bengtsson" <henrik.bengtsson using gmail.com> wrote:
> 
>      Simon's suggestion with withCallingHandlers() is the correct way.
>      Also, note that if you use tryCatch() to catch warnings, you're
>      *interrupting* the evaluation of the expression of interest, e.g.
> 
>      > res <- tryCatch({ message("hey"); warning("boom"); message("there"); 42 }, warning = function(w) { message("Warning caught: ", conditionMessage(w)); 3.14 })
>      hey
>      Warning caught: boom
>      > res
>      [1] 3.14
> 
>      Note how it never completes your expression.
> 
>      /Henrik
> 
>      On Thu, Dec 2, 2021 at 1:14 PM Simon Urbanek
>      <simon.urbanek using r-project.org> wrote:
>      >
>      >
>      > Adapted from demo(error.catching):
>      >
>      > > W=list()
>      > > withCallingHandlers(foo(), warning=function(w) { W <<- c(W, list(w)); invokeRestart("muffleWarning") })
>      > > str(W)
>      > List of 2
>      >  $ :List of 2
>      >   ..$ message: chr "warning 1"
>      >   ..$ call   : language foo()
>      >   ..- attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>      >  $ :List of 2
>      >   ..$ message: chr "warning 2"
>      >   ..$ call   : language foo()
>      >   ..- attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>      >
>      > Cheers,
>      > Simon
>      >
>      >
>      > > On Dec 3, 2021, at 10:02 AM, Fox, John <jfox using mcmaster.ca> wrote:
>      > >
>      > > Dear R-devel list members,
>      > >
>      > > Is it possible to capture more than one warning message using tryCatch()? The answer may be in ?conditions, but, if it is, I can't locate it.
>      > >
>      > > For example, in the following only the first warning message is captured and reported:
>      > >
>      > >> foo <- function(){
>      > > +   warning("warning 1")
>      > > +   warning("warning 2")
>      > > + }
>      > >
>      > >> foo()
>      > > Warning messages:
>      > > 1: In foo() : warning 1
>      > > 2: In foo() : warning 2
>      > >
>      > >> bar <- function(){
>      > > +   tryCatch(foo(), warning=function(w) print(w))
>      > > + }
>      > >
>      > >> bar()
>      > > <simpleWarning in foo(): warning 1>
>      > >
>      > > Is there a way to capture "warning 2" as well?
>      > >
>      > > Any help would be appreciated.
>      > >
>      > > John
>      > >
>      > > --
>      > > John Fox, Professor Emeritus
>      > > McMaster University
>      > > Hamilton, Ontario, Canada
>      > > Web: http://socserv.mcmaster.ca/jfox/
>      > >
>      > >
>      > >
>      > > ______________________________________________
>      > > R-devel using r-project.org mailing list
>      > > https://stat.ethz.ch/mailman/listinfo/r-devel
>      > >
>      >
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