[R] help with oop in R - class structure and syntex

[Gabor Grothendieck]

On Feb 6, 2008 9:45 AM, tom soyer <tom.soyer at gmail.com> wrote:
> Thanks Gabor for illustrating the basics oop in R using S3. Maybe I didn't
> have the right documents, but you example taught me more about oop in R than
> everything else I read combined! Thanks for the tip on R.oo, I plan to check
> it out later.
>
> I have a few followup questions...
>
> (1) how do I encapsulate the generics? i.e., if a class has 100 methods,
> then does it mean 100 generics would be dumped in the global environment?
> Or, is it possible to define a local environment and restrict the generics
> from one class to a particular environment? But then how do you call the
> generics from a special environment? Also, is it possible to inherit classes
> across different environment?

Both ofthe following return 3.  If that is not what you are asking
then I suggest you experiment with a few small examples of
this nature:

f <- function() {
    F <- function(x) UseMethod("F")
    F.default <- function(x) x
    F(3)
}
F.default <- function(x) NULL
f()


F <- function(x) UseMethod("F")
f <- function() {
    F.default <- function(x) x
    F(3)
}
F.default <- function(x) NULL
f()

>
> (2) it seems that an R specific IDE would improve productivity dramatically
> (maybe even necessary?) with respect to oop. Is there such an IDE and does
> it work for oop? I recall a group (in Germany?) was working on it but I
> can't remember where I read about it.
>
> Thanks!
>
>
> On 2/5/08, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> > This illustration uses S3.  Note that functions do not modify their
> arguments
> > so to modify an object we have to pass it to the method and then pass the
> > object back.  There is also another system called S4 which involves typing
> > of arguments and there are packages proto and R.oo which provide different
> > OO models.
> >
> >
> > # define constructors for bicycle and mountainBike classes
> > Bicycle <- function(cadence, gear, speed) structure(list(cadence =
> > cadence, gear = gear, speed = speed), class = "bicycle")
> > MountainBike <- function(cadence, gear, speed, seatHeight) {
> >   x <- Bicycle(cadence, gear, speed)
> >   x$seatHeight <- seatHeight
> >   class(x) <- c(class(x), "mountainBike")
> >   x
> > }
> >
> > # define generic setCadence and then methods for each class
> >
> > setCadence <- function(x, cadence) UseMethod("setCadence")
> > setCadence.bicycle <- function(x, cadence) { x$cadence <- cadence; x }
> >
> > # mountBike's setCadence method overrides bicycle's setCadence method
> > setCadence.mountBike <- function(x, cadence) { x$cadence <- cadence + 1; x
> }
> >
> > # list the setCadence methods avialable
> > methods(setCadence)
> >
> > # define a generic applyBrake and a "bicycle" method
> > # mountainBike will inherit the bicycle method by default
> > applyBrake <- function(x, decrement) UseMethod("applyBrake")
> > applyBrake.bicycle <- function(x, decrement) { x$speed <- x$speed -
> decrement }
> >
> > # list the applyBrake methods available
> > methods(applyBrake)
> >
> > b <- Bicycle(1, 2, 3)
> > m <- MountainBike(4, 5, 6, 7)
> > m <- applyBrake(m, 1)
> >
> >
> > On Feb 5, 2008 8:21 AM, tom soyer <tom.soyer at gmail.com> wrote:
> > > Hi,
> > >
> > > I read section 5, oop, of the R lang doc, and I am still not sure I
> > > understand how to build a class in R for oop. I thought that since I
> > > understand the oop syntex of Java and VB, I am wondering if the R
> programmig
> > > experts could help me out by comparing and contrasting the oop syntex in
> R
> > > with that of Java. For example, the basic class structure in Java is
> like
> > > this:
> > >
> > > public class Bicycle {
> > >
> > >    // *the Bicycle class has three fields*
> > >    public int cadence;
> > >    public int gear;
> > >    public int speed;
> > >
> > >    // *the Bicycle class has one constructor*
> > >    public Bicycle(int startCadence, int startSpeed, int startGear) {
> > >        gear = startGear;
> > >        cadence = startCadence;
> > >        speed = startSpeed;
> > >    }
> > >
> > >    // *the Bicycle class has four methods*
> > >    public void setCadence(int newValue) {
> > >        cadence = newValue;
> > >    }
> > >
> > >    public void setGear(int newValue) {
> > >        gear = newValue;
> > >    }
> > >
> > >    public void applyBrake(int decrement) {
> > >        speed -= decrement;
> > >    }
> > >
> > >    public void speedUp(int increment) {
> > >        speed += increment;
> > >    }
> > >
> > > }
> > >
> > > Could one of the R experts please illustrate the R class syntex for
> writing
> > > the R equivalent of the Java Bicycle class above?
> > >
> > > Also, in Java, inheritance is done like this:
> > >
> > > public class MountainBike extends Bicycle {
> > >
> > >    // *the MountainBike subclass has one field*
> > >    public int seatHeight;
> > >
> > >    // *the MountainBike subclass has one constructor*
> > >    public MountainBike(int startHeight, int startCadence, int
> startSpeed,
> > > int startGear) {
> > >        super(startCadence, startSpeed, startGear);
> > >        seatHeight = startHeight;
> > >    }
> > >
> > >    // *the MountainBike subclass has one method*
> > >    public void setHeight(int newValue) {
> > >        seatHeight = newValue;
> > >    }
> > >
> > > }
> > >
> > > What would be the R oop syntex for inheritance in the case of the
> > > MontainBike class?
> > >
> > > Thanks!
> > >
> > > --
> > > Tom
> > >
> > >        [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > R-help at 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.
> > >
> >
>
>
>
> --
> Tom