[R] Passing environments: why doesn't this work???

[Peter Dalgaard]

John Tillinghast 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?

Yes, what you do. You just missed the difference between eval and evalq 
(been there, done that, got the gray hair...)

-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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