[Rd] suppress *specific* warnings?

[Ben Bolker]

On 12-10-21 09:08 PM, 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 a warning).

  As may have been obvious, I was copying suppressWarnings() verbatim --
so I guess you'd have to ask R-core for the reasoning there ...

> 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")
>           }
>       })
>   }
> 
> 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

  Great, thank you!

> 
> 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
>>
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>>
> 
>