Re: [Rd] Defining environments within functions

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Fri, 29 Aug 2008 07:20:27 -0400

On 29/08/2008 6:52 AM, Giles Hooker wrote:
> Thanks,
>
> I think I over-emphasized the secondary function, but I can generate the
> scoping problem as follows. First, at the command line, I can get a
> function to access objects that were not in its arguments by
>
> ProfileEnv = new.env()
> hello.world = "Hello World"
> assign('hello.world',hello.world,3,envir=ProfileEnv)
>
> fn1 = function()
> {
> hw = get('hello.world',envir=ProfileEnv)
> print(hw)
> }
>
> and then call
>
> > fn1()
> [1] "Hello World"
>
>
> Now I want to define a wrapper function
>
> fn2 = function()
> {
> ProfileEnv = new.env()
> hello.world = "Hello World"
> assign('hello.world',hello.world,3,envir=ProfileEnv)
>
> fn1()
> }
>
> and if I try
>
> > rm(ProfileEnv) # Just to be safe
> > rm(hello.world)
> > fn2()
> Error in get("hello.world", envir = ProfileEnv) :
> object "ProfileEnv" not found

In fn2, you have a local variable called ProfileEnv. You defined fn1 in the global environment, so it can't see it. Everything would work if you defined fn1 within fn2.

A more natural way to do this is not to explicitly use environments. Just use the natural lexical scoping in R. In the example below, I've also added a counter variable, to answer your other question.

 > buildfn1 <- function() {

+   hello.world <- "Hello World"
+   counter <- 0
+
+   fn1 <- function() {
+     print(hello.world)
+     counter <<- counter + 1 # note superassignment <<-
+     print(counter)
+   }
+
+   return(fn1)
+ }
 >

 > fn1 <- buildfn1()
 > fn1()
[1] "Hello World"
[1] 1
 > fn1()
[1] "Hello World"
[1] 2

Duncan Murdoch

>
> In my actual code, fn1() is really a call to
>
> optim(pars,ProfileErr,....)
>
> and hello.world are quantities that were calculated the last time that
> ProfileErr was called and that I want to keep track of.
>
> As an alternative simple example, how would I keep a counter for the
> number of times that optim (or any other generic optimizer) has called
> ProfileErr?
>
> giles
>

>>> How can I define environments within a function so that they are visible
>>> to calls to a sub-function?
>>>   
>> I think you need to give a simplified, runnable example.  (Or at least 
>> runnable until it hits the scoping problem you've got.)  "Sub-function" 
>> isn't R terminology, and it's not clear what you mean by it.
>

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