Re: [R] How to share variables

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Mon 21 Aug 2006 - 18:02:08 EST

On 8/21/06, Gabor Grothendieck <ggrothendieck@gmail.com> wrote:
> On 8/21/06, Sergio Martino <s.martino@tno.it> wrote:
> > Thanks for your fast replay and sorry for my late one (I was on holidays)
> >
> > The structure I would like to emulate (the fortran common statement) is a
> > different from what you are describing.
> >
> > The examples "scoping" and the links to OO programming show the use of local
> > variable which are tied to the object itself.
> >
> > My need is to have a group of (big) variable shared among some function in a
> > way that they can be accessed freely.
> >
> > More useful is the environment example you reported. The only problem is
> > that it seems I need to replace the whole environment of the function. What
> > I need to investigate is where the variables created inside the inner
> > function (myfun) go. If they belong to the enviroment (e) I will get a
> > mix-up of variables with side effect (variables with the same name) and it
> > will be a pain.
>
> Each time myfun is run a new environment is created to hold
> its local variables. The parent of that environment is e in
> this example by construction. So e and the environment that
> is temporarily created to hold myfun's variables are distinct.

>
> Adding a couple statements to display what is in each might
> help clarify this:
>
> > e <- new.env()
> > e$dat <- 1:3
> > myfun <- function(x) {
> + cat("In current env:", ls(), "\n")
> + cat("In parent env:", ls(parent.env(environment())), "\n")
> + sum(x + dat)
> + }
> > environment(myfun) <- e
> > myfun(10) # fun can access dat
> In current env: x
> In parent env: dat
> [1] 36
>
>
> >
> > If I can use inside myfun the variable as e$dat (without changing the
> > enviroment (no environment(myfun) <- e statement)) than it will be ok.
>
> Yes you can. You can either make sure that e is visible to myfun
> via normal scoping rules or pass it explicitly:
>
> e <- new.env()
> e$dat <- 1:3
> myfun <- function(x) sum(x + e$dat)
> myfun(10)
>
> # or passing e explicitly
>
> myfun2 <- function(x, e) sum(x + e$dat)
> myfun2(10, e)
>
> # or using the proto package:to define e
> # and the same myfun and myfun2
>
> library(proto)
> e <- proto(dat = 1:3)
> myfun(10)
> myfun2(10, p)

Typo. That was supposed to be myfun2(10, e)

>
> In the above examples we used environments but these are simple
> enough that we could have used lists:
>
> e <- list(dat = 1:3)
> myfun(10) # relying on scope rules
> myfun2(10, e) # passing explicitly
>
> >
> > I need to experiment a little bit.
> >
> > Sergio
> >
> >
> >
> >
> > > On 8/2/06, Sergio Martino <s.martino@tno.it> wrote:
> > > > Hi,
> > > >
> > > > I would like to realize in R a structure like the fortran common ie a
> > way to
> > > > declare some variable that can only be accessed by all the functions
> > which
> > > > need to.
> > > >
> > > > Browsing the archive it seems that the simplest way is to declare the
> > > > variables and the functions in a big function which wraps all. But this
> > is
> > > > impratical when the functions are big.
> > >
> > > There is a demonstration of that found by issuing the command:
> > >
> > > demo(scoping)
> > >
> > > >
> > > > The environments seems to do the trick but I am not enough familiar with
> > > > them to make my ways out.
> > >
> > > Yes place your data in an environment as shown and then for
> > > each function that is to access the environment should have
> > > its environment set accordingly:
> > >
> > > e <- new.env()
> > > e$dat <- 1:3
> > > myfun <- function(x) sum(x + dat)
> > > environment(myfun) <- e
> > > myfun(10) # fun can access dat
> > >
> > > Realize that what you are trying to do is to create a sort of object
> > > oriented structure with the data being the objects and the functions
> > > being the methods. The proto package provides some functionality
> > > to implement that and also supports delegation (similar to
> > > inheritance):
> > >
> > > library(proto)
> > > package?proto # all sources of info on proto
> > >
> > > # example - create proto object p with some data dat and a method fun
> > > p <- proto(dat = 1:3, fun = function(., x) sum(x + .$dat))
> > >
> > > # invoke method
> > > p$fun(10) # runs fun. fun has access to dat
> > >
> > > # create a child q of p and run fun
> > > # q overrides dat with its own dat while inheriting fun
> > > q <- p$proto(dat = 4:6)
> > > q$fun(10)
> > >
> > > Another possibility would be to look at the R.oo package which is
> > > another object oriented infrastructure based on environments.
> > >
> > > >
> > > > Is there any example or pointers to easy but complete environment usage?
> > > >
> > > > Thanks in Advance
> > > >
> > > > Sergio Martino
> >
> >
>



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