[R] Creating an environment for a function.

[Duncan Murdoch]

On 4/13/2006 11:38 AM, Rolf Turner wrote:
> I am trying to build a function in a context where the environment
> concept would appear to be useful.  But I'm a bit foggy about this
> concept and would appreciate some pointers and advice.
> 
> Basically the function I'm building, say foo(x,t), is a function of
> two variables).  Depending on the value of t, foo will return one of
> the values f1(x), f2(x), ..., fk(x), where each of f1, ..., fk is a
> piecewise linear function (built using approxfun()).
> 
> Now I want other functions to be able to get at these pwl functions,
> making use of a syntax of the form
> 
> 		bar(y,foo)
> 
> so that in the code of bar() I could have assignments like
> 
> 		clyde <- get("f1",envir=environment(foo))
> 
> So rather than assigning f1, ..., fk in the body of foo, I would like
> to assign them in the environment of foo.
> 
> I want to do something like
> 
> 		environment(foo) <- melvin
> 
> where melvin contains f1, ..., fk.  But how do I create ``melvin''
> so that it is acceptable to the foregoing assignment?

Generally it's not necessary to explicitly set the environment.  Here 
the way to get what you want is to define f1 and foo in the same 
environment; then environment(foo) (which defaults to the environment 
where it was created) will contain f1.

So you can have a function like this:

makefoo <- function() {
   f1 <- ...
   f2 <- ...
   foo <- ...
   return(foo)
}

and the environment of the call to makefoo() will live as long as foo does.


> 
> One way I ***could*** go about it would be to create melvin
> as a list:
> 
> 		melvin <- list(f1=f1,f2=f2,etc.)
> 
> Then I could do
> 
> 		attach(melvin)
> 		environment(foo) <- as.environment(2)
> 
> This seems to work ... but it also seems unnecessarily convoluted.
> 
> I could also do
> 
> 		assign("f1",f1,envir=environment(foo))
> 		assign("f2",f2,envir=environment(foo))
> 		etc.
> 
> after creating foo(), but this is tejous.  I think I must be missing
> a point or three.  As I said, I don't really grok environments.

This is probably a bad idea, since the environment of foo (as you 
originally set it up) was likely .GlobalEnv.  So this would be 
equivalent to just having code

f1 <- ...
f2 <- ...
foo <- ...

and so on.

> Given that what I want to do makes any kind of sense at all, can
> someone start me off in the right direction.

Maybe this helped?

Duncan Murdoch