[R] passing arguments via "..."

[Bert Gunter]

Passing arguments can be tricky ( take a look at plot.default !!).
There may be a better approach then what you have considered.

hist is (S3) generic. So make a method for an S3 class that will
handle data structures like your x. Something like:

class(x ) <- c("zebra",class(x))
hist.zebra <- function(x,...)
{
########################################
## code to process x and turn it into a class for which an existing
hist method exists
## say you have turned it into y, of class "gnu" and there's an
existing hist.gnu method (use ## methods(hist) to see what already
exists). Then just :
#############################################

hist(y,...)
}

Whatever was in your original ... argument to hist.zebra will now get
passed to the ... argument of hist.gnu, which is what will be called
by the generic hist().  hist.gnu will use default argument values as
needed.

Is this what you want?

See:

AN Intro to R (have you read it?) for more on S3 methods and also

?UseMethod

-- Bert


On Tue, Mar 29, 2011 at 10:47 AM, Cable, Samuel B Civ USAF AFMC
AFRL/RVBXI <Samuel.Cable at hanscom.af.mil> wrote:
> I would like to do something like the following:
>
> Fancyhist<-function(x,...) {
>
> # first, process x into xprocess somehow, then ...
>
>  if (is.null(breaks)) {   # yes, I know this is wrong
> # define the histogram breaks somehow, then call hist:
>     hist(xprocess,breaks=breaks,...)
>  } else {
> # use breaks give in calling argument
>     hist(xprocess,...)
>  }
>
> }
>
> But, those of you who know R better than I do have already spotted that
> "is.null(breaks)" just won't work.  Neither does "exists" or "missing".
>
> I can think of ways to do this involving new arguments with new names --
> like "histbreaks" or something -- but that seems inelegant.
>
> Is there a way to do what I am trying to do here?
>
> Thanks.
>
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>



-- 
Bert Gunter
Genentech Nonclinical Biostatistics