[R] Convert numerical value into function which returns numerical value

[William Dunlap]

You can make such functions by using the fact that a function
(really, a 'closure') always has access to the environment in
which the function was created.  E.g.
  makeConstantFunction <- function(constant) {
      force(constant) # evaluate the argument now
      function(PAI) {
          constant
      }
  }
  f17 <- makeConstantFunction(17)
  flog17 <- makeConstantFunction(log(17))
  f17(111)
  # [1] 17
  flog17(111)
  # [1] 2.833213

If you print f17 and flog17 they will look the same, except for
their environments and you have to inspect those to see why
they act differently.

  ls.str(environment(f17))
  # constant :  num 17
  ls.str(environment(flog17))
  # constant :  num 2.83

If you really want the functions to look different you can use
substittute or bquote, but that is also a bit mysterious (you need the
eval()
their outputs):
  g17 <- eval(substitute(function(PAI)x, list(x=17)))
  h17 <- eval(bquote(function(PAI).(x), list(x=17)))
  g17(10)
  [1] 17
  h17(10:1)
  [1] 17




Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Thu, Apr 9, 2015 at 5:39 AM, Rainer M Krug <Rainer at krugs.de> wrote:

>
> Hi
>
> I want convert, in a function, an argument from a numerical value to a
> function which returns this value.:
>
> My Code:
>
> --8<---------------cut here---------------start------------->8---
> dep <- 13
> dep <- function() {dep}
> dep
> --8<---------------cut here---------------end--------------->8---
>
> This is what I get:
> #+RESULTS:
> ,----
> | function(PAI) { dep }
> `----
>
> This is what I want
> ,----
> | function(PAI) { 13 }
> `----
>
> I thought about using eval(dep), but this gives me the effectively the
> same.
>
> Is it possible to achieve what I want? I somehow have the feeling this
> is not that easily possible, as the code in the function definition is
> only evaluated when the function is evaluated.
>
> I could obviously do something like
>
> --8<---------------cut here---------------start------------->8---
> dep <- 13
> depVal <- dep
> dep <- function() {depVal}
> dep()
> --8<---------------cut here---------------end--------------->8---
>
> But is there a better solution?
>
> Thanks,
>
> Rainer
>
> --
> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
> Biology, UCT), Dipl. Phys. (Germany)
>
> Centre of Excellence for Invasion Biology
> Stellenbosch University
> South Africa
>
> Tel :       +33 - (0)9 53 10 27 44
> Cell:       +33 - (0)6 85 62 59 98
> Fax :       +33 - (0)9 58 10 27 44
>
> Fax (D):    +49 - (0)3 21 21 25 22 44
>
> email:      Rainer at krugs.de
>
> Skype:      RMkrug
>
> PGP: 0x0F52F982
>
> ______________________________________________
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