[R] Display warning only once in session

[William Dunlap]

You could use local() to associate a state variable with your function:
   myFunc <- local({
       notWarnedYet <- TRUE
       function(x) {
           if (notWarnedYet) {
               warning("myFunc is funky")
               notWarnedYet <<- FALSE # note use of <<-
           }
           sqrt(log2(x))
      }
   })
E.g.,
   > myFunc(1:5)
   [1] 0.000000 1.000000 1.258953 1.414214 1.523787
   Warning message:
   In myFunc(1:5) : myFunc is funky
   > myFunc(1:5)
   [1] 0.000000 1.000000 1.258953 1.414214 1.523787
   > myFunc(1:5)
   [1] 0.000000 1.000000 1.258953 1.414214 1.523787

Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Mon, Aug 25, 2014 at 2:05 PM, Berry Boessenkool
<berryboessenkool at hotmail.com> wrote:
>
> Hi,
>
> I'm writing a function that gives a warning in a certain scenario.
> Reading this once per R session will be enough.
> i.e. it's not necessary to be shown in subsequent function calls.
>
> What's the best way to implement this?
> Some package-specific option?
> Where would I find good information on that?
>
> searching with the keywords I'm using as the subject of this message didn't dig up any results.
> Maybe it will be enough to give me some better keywords...
>
> Thanks ahead,
> Berry
>
> RclickHandbuch.wordpress.com
>
>
>
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