[Rd] Return function from function with minimal environment

[Gabor Grothendieck]

On 4/4/06, Henrik Bengtsson <hb at maths.lth.se> wrote:
> On 4/4/06, Thomas Lumley <tlumley at u.washington.edu> wrote:
> > On Tue, 4 Apr 2006, Henrik Bengtsson wrote:
> >
> > > Hi,
> > >
> > > this relates to the question "How to set a former environment?" asked
> > > yesterday.  What is the best way to to return a function with a
> > > minimal environment from a function? Here is a dummy example:
> > >
> > > foo <- function(huge) {
> > >  scale <- mean(huge)
> > >  function(x) { scale * x }
> > > }
> > >
> > > fcn <- foo(1:10e5)
> > >
> > > The problem with this approach is that the environment of 'fcn' does
> > > not only hold 'scale' but also the memory consuming object 'huge',
> > > i.e.
> > >
> > > env <- environment(fcn)
> > > ll(envir=env)  # ll() from R.oo
> > > #   member data.class dimension object.size
> > > # 1   huge    numeric   1000000     4000028
> > > # 2  scale    numeric         1          36
> > >
> > > save(env, file="temp.RData")
> > > file.info("temp.RData")$size
> > > # [1] 2007624
> > >
> > > I generate quite a few of these and my 'huge' objects are of order
> > > 100Mb, and I want to keep memory usage as well as file sizes to a
> > > minimum.  What I do now, is to remove variable from the local
> > > environment of 'foo' before returning, i.e.
> > >
> > > foo2 <- function(huge) {
> > >  scale <- mean(huge)
> > >  rm(huge)
> > >  function(x) { scale * x }
> > > }
> > >
> > > fcn <- foo2(1:10e5)
> > > env <- environment(fcn)
> > > ll(envir=env)
> > > #   member data.class dimension object.size
> > > # 1  scale    numeric         1          36
> > >
> > > save(env, file="temp.RData")
> > > file.info("temp.RData")$size
> > > # [1] 156
> > >
> > > Since my "foo" functions are complicated and contains many local
> > > variables, it becomes tedious to identify and remove all of them, so
> > > instead I try:
> > >
> > > foo3 <- function(huge) {
> > >  scale <- mean(huge);
> > >  env <- new.env();
> > >  assign("scale", scale, envir=env);
> > >  bar <- function(x) { scale * x };
> > >  environment(bar) <- env;
> > >  bar;
> > > }
> > >
> > > fcn <- foo3(1:10e5)
> > >
> > > But,
> > >
> > > env <- environment(fcn)
> > > save(env, file="temp.RData");
> > > file.info("temp.RData")$size
> > > # [1] 2007720
> > >
> > > When I try to set the parent environment of 'env' to emptyenv(), it
> > > does not work, e.g.
> > >
> > > fcn(2)
> > > # Error in fcn(2) : attempt to apply non-function
> > >
> > > but with the new.env(parent=baseenv()) it works fine. The "base"
> > > environment has the empty environment as a parent.  So, I try to do
> > > the same myself, i.e. new.env(parent=new.env(parent=emptyenv())), but
> > > once again I get
> >
> > I don't think you want to remove baseenv() from the environment. If you
> > do, no functions from baseenv will be visible inside fcn. These include
> > "{" and "*", which are necessary for your function. I think the error
> > message comes from being unable to find "{".
>
> Thank you, this makes sense. Modifying Roger Peng's example
> illustrates what you say:
>
> foo <- function(huge) {
>        scale <- mean(huge)
>        g <- function(x) x
>        environment(g) <- emptyenv()
>        g
> }
>
> fcn <- foo(1:10e5)
> fcn(2)
> # [1] 2
>
> But as soon as you add "something" to the g(), it is missing;
>
> foo <- function(huge) {
>        scale <- mean(huge)
>        g <- function(x) { x }
>        environment(g) <- emptyenv()
>        g
> }
>
> fcn <- foo(1:10e5)
> fcn(2)
> # Error in fcn(2) : attempt to apply non-function
>
> ...and I did not know that "{" and "(" are primitive functions.  Interesting.
>
> I conclude that 'env <- new.env(parent=baseenv())' is better than
> ''env <- new.env()' in my case.

Is there any reason to use

   env <- new.env(parent=baseenv())

instead of just

   env <- baseenv() ?

The extra environment being created seems to serve no purpose.