[R] Fwd: Evaluating a function within a pre-defined environment?

[Gabor Grothendieck]

You could write a wrapper function that accepts the output of the
function you don't want to change and then sets the values.

# f is function we don't want to change
f <- function(a)  x + a

wrapper <- function(x, e) {
   environment(f) <- e
   e$x <- f(x)
}

e <- new.env()
e$x <- 2
wrapper(3, e)
e$x # 5

or with proto:

library(proto)
p <- proto(x = 2, f = f, wrapper = function(this, x) this$x <-
with(this, f)(x) )
p$wrapper(3)
p$x # 5




On Wed, Dec 9, 2009 at 5:48 PM, David Reiss <dreiss at systemsbiology.org> wrote:
> Ideally I would like to be able to use the function f (in my example)
> as-is, without having to designate the environment as an argument, or
> to otherwise have to use "e$x" in the function body.
>
> thanks for any further advice...
>
> On Wed, Dec 9, 2009 at 2:36 PM, Gabor Grothendieck
> <ggrothendieck at gmail.com> wrote:
>> e <- new.env()
>> e$x <- 2
>> f <- function(a, e) { e$x <- e$x + a; e$x }
>> f(3, e)
>> e$x # 5
>>
>> Another way to accomplish this is to use the proto package which puts
>> the whole thing into an object oriented framework.  See
>> http://r-proto.googlecode.com
>>
>> library(proto)
>> p <- proto(x = 2, f = function(this, a) { this$x <- this$x + a; this$x })
>> p$f(3) # 5
>>
>>
>> On Wed, Dec 9, 2009 at 4:54 PM, David Reiss <dreiss at systemsbiology.org> wrote:
>>> Hi all,
>>>
>>> I have a somewhat confusing question that I was wondering if someone
>>> could help with. I have a pre-defined environment with some variables,
>>> and I would like to define a function, such that when it is called, it
>>> actually manipulates the variables in that environment, leaving them
>>> to be examined later. I see from the R language definition that
>>>
>>> "When a function is called, a new environment (called the evaluation
>>> environment) is created, whose enclosure (see Environment objects) is
>>> the environment from the function closure. This new environment is
>>> initially populated with the unevaluated arguments to the function; as
>>> evaluation proceeds, local variables are created within it."
>>>
>>> So basically, I think I am asking if it is possible to pre-create my
>>> own "evaluation environment" and have it retain the state that it was
>>> in at the end of the function call?
>>>
>>> Example:
>>>
>>> e <- new.env()
>>> e$x <- 3
>>> f <- function(xx) x <- x + xx
>>>
>>> can I then call f(2) and have it leave e$x at 5 after the function
>>> returns? I know that
>>>
>>> environment(f) <- e
>>>
>>> goes part of the way, but I would like to let the function also write
>>> to the environment.
>>>
>>> Thanks for any advice.
>>>
>>> --David
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>