[Rd] Capturing all warnings (with messages)

Wed Feb 4 20:19:01 CET 2009

Jon Clayden wrote on 02/04/2009 12:11 PM:
> Dear Jeff,
> 
> Many thanks for the suggestion, but I don't think tryCatch() is the
> answer, mainly because it causes code to stop executing when a warning
> is signalled:
> 
>> f <- function(w) print(w$message)
>> tryCatch({warning("Test"); print(3)},warning=f)
> [1] "Test"
> 
> (The "print(3)" call is not run.) In this regard,
> withCallingHandlers() is preferable. But either way it is untidy, at
> best, to routinely put code inside one of these functions when I know
> I always want to handle warnings my way. If I could set an appropriate
> option when a package is loaded, or in an .Rprofile, then I should
> never need to worry about whether a bit of code might generate
> warnings and so should be wrapped.

So you want your program to handle all warnings your way, but you want 
to continue execution after you have trapped the warnings. What 
specifically do you want your program to do with a warning once you know 
what it is?

(I'd like to help you work through your problem to a solution because I 
selfishly want to learn more about R's condition and restart system for 
rapache's sake, my personal project. Right now, the way rapache notifies 
users of R warnings and errors is crude but works.)

Jeff

> 
> Regards,
> Jon
> 
> 2009/2/4 Jeffrey Horner <jeff.horner at vanderbilt.edu>:
>> Jon Clayden wrote on 02/04/2009 06:59 AM:
>>> Dear all,
>>>
>>> For an open-source project that I'm working on (1), which uses R for all
>>> its heavy lifting but includes a wrapper shell script, I was hoping to find
>>> a way to capture all warnings (and, in fact, errors too), and handle them in
>>> my own way. I realise I can do this for a single expression using something
>>> like:
>>>
>>>  > f <- function(w) print(w$message)
>>>  > withCallingHandlers(warning("Test"),warning=f)
>>> [1] "Test"
>>> Warning message:
>>> In withCallingHandlers(warning("Test"), warning = f) : Test
>>>
>>> But I would like to capture all warnings, globally. The
>>> "warning.expression" option doesn't seem to allow an argument, and I can't
>>> seem to use "last.warning" to get at the message either:
>>>
>>>  > g <- function() print(last.warning$message)
>>>  > options(warning.expression=quote(g()))
>>>  > warning("Test2")
>>> NULL
>>>
>>> Could anyone tell me whether there's a way to do this, please? An old
>>> thread on this topic seemed to go unresolved (2), and I've skimmed RNEWS and
>>> I don't see anything about this since then.
>> In fact, the thread did have the answer: tryCatch(). The help page is a bear
>> to read and comprehend, but if you do invest the time it should convince you
>> that you will want to use it. I find that I have to read and reread many
>> sections of R documentation before I can reconcile what I want to know with
>> what the authors are trying to tell me.
>>
>> I don't comprehend everything about R's condition system, but let me see if
>> I can convince you that you need tryCatch() to do what you want.
>>
>> Consider:
>>
>> x <- function() warning("warning message")
>> y <- function() call_unknown_fun()
>> z <- function() message('message message')
>>
>> Each of these functions signal conditions of a particular condition class:
>> simpleWarning, simpleError, and simpleMessage, respectively.
>>
>> w <- function(e) str(e)
>>
>> I'm going to use w  to trap the simpleWarning condition:
>>
>>> tryCatch(x(),simpleWarning=w)
>> List of 2
>>  $ message: chr "warning message"
>>  $ call   : language x()
>>  - attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>>
>> So tryCatch returned a list with two elements, the message and the call that
>> signaled the condition. In fact the list is actually an S3 object of class
>> simpleWarning, which inherits from warning and condition. Reading the help
>> page for tryCatch(), I can actually do this:
>>
>>> tryCatch(x(),condition=w)
>> List of 2
>>  $ message: chr "warning message"
>>  $ call   : language x()
>>  - attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>>
>> since simpleWarning inherits from condition. And in fact I can use the
>> condition class to trap everything I want.
>>
>>> tryCatch(y(),condition=w)
>> List of 2
>>  $ message: chr "could not find function \"call_unknown_fun\""
>>  $ call   : language y()
>>  - attr(*, "class")= chr [1:3] "simpleError" "error" "condition"
>>
>>> tryCatch(z(),condition=w)
>> List of 2
>>  $ message: chr "message message\n"
>>  $ call   : language message("message message")
>>  - attr(*, "class")= chr [1:3] "condition" "message" "simpleMessage"
>>
>> (Side note: is the class hierarchy actually correct for this simpleMessage
>> object?)
>>
>> So in summary, wrap every R expression you want to run within a single
>> tryCatch() call and trap all conditions with one handler for the abstract
>> class named 'condition'. I think that's what you want...
>>
>> Jeff
>>
>>
>>>  > sessionInfo()
>>> R version 2.8.1 (2008-12-22)
>>> i386-apple-darwin8.11.1
>>>
>>> locale:
>>> en_GB.UTF-8/en_US.UTF-8/C/C/en_GB.UTF-8/en_GB.UTF-8
>>>
>>> attached base packages:
>>> [1] stats     graphics  grDevices utils     datasets  splines   methods
>>> [8] base
>>>
>>> other attached packages:
>>> [1] tractor.session_1.0.0   tractor.base_1.0.3      tractor.nt_1.0.2
>>>
>>> loaded via a namespace (and not attached):
>>> [1] tools_2.8.1
>>>
>>> Regards,
>>> Jon
>>>
>>>
>>> (1) http://code.google.com/p/tractor/
>>> (2) http://finzi.psych.upenn.edu/R/Rhelp02/archive/61872.html
>>>
>>>
>>> --
>>> Jonathan D. Clayden, Ph.D.
>>> Research Fellow
>>> Radiology and Physics Unit
>>> UCL Institute of Child Health
>>> 30 Guilford Street
>>> LONDON  WC1N 1EH
>>> United Kingdom
>>>
>>> t | +44 (0)20 7905 2708
>>> f | +44 (0)20 7905 2358
>>> w | www.homepages.ucl.ac.uk/~sejjjd2/
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>> --
>> http://biostat.mc.vanderbilt.edu/JeffreyHorner
>>
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-- 
http://biostat.mc.vanderbilt.edu/JeffreyHorner