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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