On Thu, Jan 13, 2011 at 6:46 AM, Martin Morgan <mtmor...@fhcrc.org> wrote:
> On 01/12/2011 10:54 PM, steven mosher wrote:
> > I have J Chambers wonderful text ( Software for data Analysis) and I've
> been
> > trying
> > my hand at some very routine S4 OOP development.
> >
> > One of the things I was trying to do was to create some very basic S4
> > classes. The first
> > was simply a class that had a data.frame as part of its representation.
> >
> > setClass("df",representation(dirframe="data.frame"))
> >
> > The object basically contains a data.frame that represents a file
> directory
> > listing
> > with a column named filename, size, time, etc.
> >
> > And then I have methods for doing various things with this object.
> >
> > I then tried to tackle the problem of coercing this S4 object to a
> > data.frame. Again just a learning exercise.
> >
> > The goal would be able to make a call like this
> >
> > testFrame <- as.data.frame(x)
> >
> > where x, was an object of class "df"
> >
> > If I try to define "as.data.frame" as a S4 method, then I can make it
> work,
> > but I then destroy the S3 functionality
> > of as.data.frame, so that if I were to try to coerce a matrix to a
> > data.frame it would work.
>
> Hi Steven --
>
> This works for me
>
> setClass("A", representation=representation(df="data.frame"))
>
> setMethod("as.data.frame", "A",
> function(x, row.names=NULL, optional=FALSE, ...)
> {
> ## implementation, e.g.,
> callGeneric(x@df, row.names=row.names, optional=optional, ...)
> })
>
this makes no sense to me.
Looking at this in the manual:
"A call to callGeneric can only appear inside a method definition. It then
results in a call to the current generic function. The value of that call is
the value of callGeneric. While it can be called from any method, it is
useful and typically used in methods for group generic functions."
I'm further confused. what is the "current" generic function?
>
> > as.data.frame(new("A"))
> Object of class "data.frame"
> data frame with 0 columns and 0 rows
> > as.data.frame(matrix(0, 3, 5))
> V1 V2 V3 V4 V5
> 1 0 0 0 0 0
> 2 0 0 0 0 0
> 3 0 0 0 0 0
>
>
> Maybe you call setGeneric (no need to, setMethod will promote
> as.data.frame automatically) in a way that does not specify the default
> (arg useAsDefault) correctly?
>
I think that may have been the mistake.. what do you mean by
no need to call setGeneric?
I really like chambers book, but there are certain parts where the lack of
simple examples
really makes it difficult to follow.
>
> Martin
>
>
> >
> >
> > So, I guess my question is what do I do, write an s3 method for
> > as.data.frame that takes a "df" object as a paramter?
> > The book wasn't exactly clear ( or I'm not that bright), or is there a
> way
> > to make the S4 method I wrote "as.data.frame"
> > call the S3 method if needed?
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
> --
> 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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