[R] Passing environments: why doesn't this work???
Gabor Grothendieck
ggrothendieck at gmail.com
Sun Feb 15 21:47:11 CET 2009
Note that you can do things like this too:
env$x
with(env, x^2)
Also its possible you are really getting into object oriented
programming without realizing it with the your environments
being the objects your functions being the methods. In that
case check out the proto package which formalizes all this
using environments to implement the prototype model (also
called object-based model) of object oriented programming.
http://r-proto.googlecode.com
On Sun, Feb 15, 2009 at 3:17 PM, John Tillinghast <tilling at gmail.com> wrote:
> This is a trivial example I set up to see if I could pass an environment and
> use the variables in it
> (this is for a function that will be called many times and might need to use
> a lot of variables that
> won't be changing, so it seemed more sensible to use an environment).
>
> Here's the code:
> #########################
> #The outer function
> run.internal.env <- function(x) {
> in.env <- new.env()
> assign('x', x, envir=in.env)
> print(eval(x^2, envir=in.env))
> print(ls(envir=in.env))
> return(use.internal.env(in.env))
> }
>
> #The inner function
> use.internal.env <- function(env) {
> print(ls(envir=env))
> return(eval(x^2, envir=env))
> }
> ##########################
> Now if I type
>
> run.internal.env(2), my output looks like
>
> [1] 4 [This is the evaluation in the outer routine]
> [1] "x" [This is the "ls" from the outer routine]
> [1] "x" [This is the "ls" from the inner routine]
> Error in eval(x^2, envir=env): object "x" not found [??? It was listed, so
> why can't it be evaluated???]
>
> If there's anything called "x" in the global environment, it will evaluate
> that x^2 instead, e.g.
> x <- 1:3
> run.internal.env(2)
> [1] 4 [This is the evaluation in the outer routine]
> [1] "x" [This is the "ls" from the outer routine]
> [1] "x" [This is the "ls" from the inner routine]
> [1] 1 4 9
>
> Is there any way to force it to use the environment I actually want, and
> keep all the values I assigned in there?
>
> [[alternative HTML version deleted]]
>
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