Re: [R] Referring to objects themselves

From: Russ Abbott <russ.abbott_at_gmail.com>
Date: Sat, 19 Mar 2011 21:10:15 -0700

Actually I'm a big Haskell fan. So I think of functional programming very positively. However, the environment() function doesn't seem to be treated functionally. If I write

    this <- environment()
at the top of the previous example, the other functions and the variables they are bound to are inserted into the environment which had already been bound to 'this' afterwards.

In fact, even when it is left at the end that line inserts 'this' into the environment, which strictly speaking it shouldn't do. So there seem to be some not-quite-functional processes going on.

*-- Russ*

On Sat, Mar 19, 2011 at 8:56 PM, Henrik Bengtsson <hb_at_biostat.ucsf.edu>wrote:

> For most standard things we do in R, one do not need this feature. R
> is a functional language. Everything is passed around as
> pass-by-value (but in a smart way so that under the hood you get
> pass-by-reference in most cases). Reference variables become useful
> first when you for instance have more complex and larger objects, and
> also when you work toward external resources, e.g. data bases,
> persistent memory, web sites etc.
>
> If you need true pass-by-reference, it is possible to obtain this in R
> at a low-resolution granularity, which means, you can do it for basic
> R data types (vectors, lists, ...) but not (really) for single
> elements of such data types. In R the 'environment' data type acts as
> a container for other data types. You can update the objects inside
> the environment and pass it around as if it was a reference variable.
>
> As already suggested, the proto and the R.oo packages utilize
> environment. Recently Reference Classes joined and is now part of
> core R. (There are other difference between these too.)
>
> So, if you're new to R and don't really need reference variables (most
> people don't), rethink how you think of classes and objects in R (=
> think functional language). Though, you would learn lots by playing
> around with environments and scopes and R's method dispatching
> mechanisms.
>
> /Henrik
>
> On Sat, Mar 19, 2011 at 6:45 PM, Russ Abbott <russ.abbott_at_gmail.com>
> wrote:
> > Thanks for all the suggestions. I realize that this isn't the most
> important
> > thing in the world -- and as a newcomer to R I gather it's not the way
> most
> > people use R anyway.
> >
> > But I tried to do what looked like the simplest suggestion.
> >
> > open.account.2 <- function(total) {
> > this <- environment()
> > list(
> > deposit = function(amount) {
> > if(amount <= 0)
> > stop("Deposits must be positive!\n")
> > total <<- total + amount
> > cat(amount, "deposited. Your balance is", this$balance(),
> > "\n\n")
> > },
> > withdraw = function(amount) {
> > if(amount > total)
> > stop("You don't have that much money!\n")
> > total <<- total - amount
> > cat(amount, "withdrawn. Your balance is", this$balance(),
> > "\n\n")
> > },
> > balance = function() {
> > cat("Your balance is", this$total, "\n\n")
> > }
> > )
> > }
> >
> > When I ran it, this is what happened.
> >
> >> x <- open.account.2(100)

> >> x$balance()
> >
> > Your balance is 100
> >
> > OK so far. But
> >
> >> x$deposit(50)
> > Error in cat(amount, "deposited. Your balance is", this$balance(),
> "\n\n")
> > :
> > attempt to apply non-function
> >
> >
> > Am I doing this the wrong way?
> >
> > Thanks for your interest.
> >
> > *-- Russ *
> >
> >
> >
> > On Sat, Mar 19, 2011 at 6:33 PM, Bert Gunter <gunter.berton_at_gene.com>
> wrote:
> >
> >> See also the proto package, I believe.
> >>
> >> -- Bert
> >>
> >> On Sat, Mar 19, 2011 at 5:51 PM, Janko Thyson
> >> <janko.thyson.rstuff_at_googlemail.com> wrote:
> >> > You might want to check out Reference Classes (?SetRefClass). The
> object
> >> > itself is stored in '.self' and can be referenced that way.
> >> >
> >> > HTH,
> >> > Janko
> >> >
> >> > -----Ursprüngliche Nachricht-----
> >> > Von: r-help-bounces_at_r-project.org [mailto:
> r-help-bounces_at_r-project.org]
> >> Im
> >> > Auftrag von Russ Abbott
> >> > Gesendet: Samstag, 19. März 2011 23:35
> >> > An: r-help_at_r-project.org
> >> > Betreff: [R] Referring to objects themselves
> >> >
> >> > Is it possible to refer to an object from within a method, as in *this
> >> *in
> >> > Java? I can't find anything about this in the documentation. Sorry
> if
> >> > I
> >> > missed it.
> >> >
> >> > Thanks.
> >> >
> >> > *-- Russ Abbott*
> >> > *_____________________________________________*
> >> > *** Professor, Computer Science*
> >> > * California State University, Los Angeles*
> >> >
> >> > * Google voice: 747-*999-5105
> >> > * blog: *http://russabbott.blogspot.com/
> >> > vita: http://sites.google.com/site/russabbott/
> >> > *_____________________________________________*
> >> >
> >> > [[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.
> >> >
> >> > ______________________________________________
> >> > 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.
> >> >
> >>
> >>
> >>
> >> --
> >> Bert Gunter
> >> Genentech Nonclinical Biostatistics
> >>
> >
> > [[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.
> >
> >
>

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