[Rd] suppress *specific* warnings?

[Martin Morgan]

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). 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

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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