Dear Martin,
I could not entirely follow your suggestion.
I can see how you define two classes inheriting from TypeOfSample, and how
these two
classes have two associated methods (incidentally, I'm unfamiliar with the:
function(type,x=numeric(),...)to do.
J
expression. What is type?
But then I'm lost. I wouldn't know how to carry on from here.
I don't know if I have explained the key point clear enough before. For the
person using
"newsample" it makes sense which name (x or y or z, etc) is used.
newsample(x=12.4) would
give something different from newsample(y=12.4); and yet another result would
be obtained if
using a combination, like newsample(x=12.4,y=12.4).
I wanted to use a simple function with default values at first, but I'm in the
middle of developing
a package using S4 formalism. I'm not sure this would be a wise thing
________________________________________
Sent: 14 February 2012 17:00
To: Foadi, James (Imperial Coll.,RAL,DIA)
Cc: r-devel@r-project.org
Subject: Re: [Rd] method using several (and different) arguments in turn
On 02/14/2012 08:43 AM, james.fo...@diamond.ac.uk wrote:
> Dear R-developers community, I have the following generic:
>
> setGeneric(
> name="newsample",
>
> def=function(x,y,z,a,b,c,...){standardGeneric("newsample")}
>
> And I can build several methods for this generic. One useful thing is to use
> "newsample"
> with only one of the 6 arguments listed. At the moment this is what I do:
>
> setMethod(
> f="newsample",
>
> signature=c("missing","missing","numeric","missing","missing","missing"),
> function(x,y,z,a,b,c,...)
> {
> ..............................
> ..............................
>
> }
> )
>
> This would be used when the single argument is z:
>
> newsample(z=12.5)
>
> To use newsample with another argument (say x) I should implement the same as
> before,
> but with signature
> c("numeric","missing","missing","missing","missing","missing").
> Is there another shorter and easier way to do this?
Hi James --
A matter of opinion, but multiple dispatch like this can be very
complicated, e.g., figuring out the 'next' method when dispatching on
two or more arguments; I'd really discourage it.
A different approach, assuming that x, y, z, ... are all numeric() but
that the sample to be drawn differs, is to define a small class
hierarchy to be used for dispatch.
setClass("TypeOfSample")
setClass("XSample", contains="TypeOfSample")
XSample <- new("XSample") ## a 'singleton', used for dispatch
setClass("YSample", contains="TypeOfSample")
YSample <- new("YSample")
and then
setGeneric("newsample",
function(type, x=numeric(), ...) standardGeneric("newsample"),
signature="type")
setMethod("newsample", "XSample", function(type, x=numeric(), ...) {
"XSample"
})
setMethod("newsample", "YSample", function(type, x=numeric(), ...) {
"YSample"
})
One could implement a default method on "TypeOfSample", and use
callNextMethod() after initial transformation, if that were the pattern.
To use:
newsample(XSample, x=1:100)
Martin
>
>
> J
>
--
Computational Biology
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109
Location: M1-B861
Telephone: 206 667-2793
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