[Rd] suppress *specific* warnings?

[Martin Morgan]

On 10/22/2012 09:57 AM, luke-tierney at uiowa.edu wrote:
> On Sun, 21 Oct 2012, Martin Morgan wrote:
>
>> On 10/21/2012 12:28 PM, Ben Bolker wrote:
>>>
>>>    Not desperately important, but nice to have and possibly of use to
>>> others, is the ability to suppress specific warnings rather than
>>> suppressing warnings indiscriminately.  I often know of a specific
>>> warning that I want to ignore (because I know that's it's a false
>>> positive/ignorable), but the current design of suppressWarnings() forces
>>> me to ignore *any* warnings coming from the expression.
>>>
>>>    I started to write a new version that would check and, if supplied
>>> with a regular expression, would only block matching warnings and
>>> otherwise would produce the warnings as usual, but I don't quite know
>>> enough about what I'm doing: see ??? in expression below.
>>>
>>>    Can anyone help, or suggest pointers to relevant
>>> examples/documentation (I've looked at demo(error.catching), which isn't
>>> helping me ... ?)
>>>
>>> suppressWarnings2 <- function(expr,regex=NULL) {
>>>      opts <- options(warn = -1)
>>>      on.exit(options(opts))
>>
>> I'm not really sure what the options(warn=-1) is doing there, maybe its for
>> efficiency to avoid generating a warning message (as distinct from signalling
>
> The sources in srs/library/base/conditions.R have
>
> suppressWarnings <- function(expr) {
>      ops <- options(warn = -1) ## FIXME: temporary hack until R_tryEval
>      on.exit(options(ops))     ## calls are removed from methods code
>      withCallingHandlers(expr,
>                          warning=function(w)
>                              invokeRestart("muffleWarning"))
> }
>
> I uspect we have still not entirely eliminated R_tryEval in this context
> but I'm not sure. Will check when I get a chance.
>
>> a warning). I think you're after something like
>>
>>  suppressWarnings2 <-
>>      function(expr, regex=character())
>>  {
>>      withCallingHandlers(expr, warning=function(w) {
>>          if (length(regex) == 1 && length(grep(regex, conditionMessage(w)))) {
>>              invokeRestart("muffleWarning")
>>          }
>>      })
>>  }
>
> A problem with using expression matching is of course that this fails
> with internationalized messages. Ideally warnings should be signaled as
> warning conditions of a particular class, and that class can be used
> to discriminate. Unfortunately very few warnings are designed this way.

Probably specific messages, rather than patterns, would be handled and then

   suppressWarnings2 <- function(expr, messages = character())
   {
       opts <- options(warn = -1)
       on.exit(options(ops))
       withCallingHandlers(expr, warning=function(w) {
           if (conditionMessage(w) %in% messages)
               invokeRestart("muffleWarning")
       })
   }

gives one the illusion of speaking many languages

   suppressWarnings2(log(-1), gettext("NaNs introduced", domain="R"))

Martin

>
> Best,
>
> luke
>
>>
>> If the  restart isn't invoked, then the next handler is called and the warning
>> is handled as normal. So with
>>
>>  f <- function() {
>>      warning("oops")
>>      2
>>  }
>>
>> there is
>>
>>> suppressWarnings2(f())
>> [1] 2
>> Warning message:
>> In f() : oops
>>> suppressWarnings2(f(), "oops")
>> [1] 2
>>
>> For your own code I think a better strategy is to create a sub-class of
>> warnings that can be handled differently
>>
>>  mywarn <-
>>      function(..., call.=TRUE, immediate.=FALSE, domain=NULL)
>>  {
>>      msg <- .makeMessage(..., domain=domain, appendLF=FALSE)
>>      call <- NULL
>>      if (call.)
>>          call <- sys.call(1L)
>>      class <- c("silencable", "simpleWarning",  "warning", "condition")
>>      cond <- structure(list(message=msg, call=call), class=class)
>>      warning(cond)
>>  }
>>
>>  suppressWarnings3 <-
>>          function(expr)
>>  {
>>      withCallingHandlers(expr, silencable=function(w) {
>>          invokeRestart("muffleWarning")
>>      })
>>  }
>>
>> then with
>>
>>  g <- function() {
>>      mywarn("oops")
>>      3
>>  }
>>
>>> suppressWarnings3(f())
>> [1] 2
>> Warning message:
>> In f() : oops
>>> g()
>> [1] 3
>> Warning message:
>> In g() : oops
>>> suppressWarnings3(g())
>> [1] 3
>>
>>>      withCallingHandlers(expr, warning = function(w) {
>>>          ## browser()
>>>          if (is.null(regex) || grepl(w[["message"]],regex)) {
>>>              invokeRestart("muffleWarning")
>>>          } else {
>>>              ## ? what do I here to get the warning issued?
>>>              ## browser()
>>>              ## computeRestarts() shows "browser",
>>>              ##    "muffleWarning", and "abort" ...
>>>              options(opts)
>>>              warning(w$message)
>>>              ## how can I get back from here to the calling point
>>>              ##   *without* muffling warnings ... ?
>>>          }
>>>      })
>>> }
>>>
>>> suppressWarnings2(sqrt(-1))
>>> suppressWarnings2(sqrt(-1),"abc")
>>>
>>>    It seems to me I'd like to have a restart option that just returns to
>>> the point where the warning was caught, *without* muffling warnings ...
>>> ?  But I don't quite understand how to set one up ...
>>>
>>>    Ben Bolker
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>
>>
>>
>


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