[Rd] Return function from function with minimal environment

From: Henrik Bengtsson <hb_at_maths.lth.se>
Date: Tue 04 Apr 2006 - 13:40:36 GMT


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

fcn(2)
# Error in fcn(2) : attempt to apply non-function

Apparently, I do not understand enough here. Please, enlighten me. In the meantime I stick with foo2().

Best,

Henrik



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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Wed Apr 05 00:09:54 2006

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