[R] Function to Define a Function

[Gabor Grothendieck]

On Mon, Aug 9, 2010 at 9:31 PM, Derek Ogle <DOgle at northland.edu> wrote:
> I am trying to define a general R function that has a function as the output that depends on the user's input arguments (this may make more sense by looking at the toy example below).  My real use for this type of code is to allow a user to choose from many parameterizations of the same general model.
>
> My "issue" is that when I compile a package with this type of code in it I get a __warning__ that "multiple local function definitions for 'm' with different formal arguments."  While this is not a "deadly error" I would like to avoid the warning if possible.  Can someone provide some guidance?  Thank you in advance for any help you can offer.
>
> For what it is worth ... I am working on a Windows XP machine with R 2.11.1.
>
>
>
>
> ## A function that allows the user to create a new function that depends on their
> ##   choice in the type argument.  As a simple example, if the user chooses "one"
> ##   then the output function is exponential growth, if the user choses "two" then
> ##   thhe output function is logistic growth.
>
> mdlChooser <- function(type=c("one","two")) {
>  type <- match.arg(type)
>  switch(type,
>    one={ m <- function(x,N0,r) N0*exp(x*r) },
>    two={ m <- function(x,N0,r,K) (N0*K)/(N0+(K-N0)*exp(-x*r)) },
>  )
>  m
> }
>
> ## define time steps
> t <- 0:10
>
> ## create a function -- junk1 -- that produces exponential growth
> junk1 <- mdlChooser("one")
> junk1
> res1 <- junk1(t,500,0.2)
> res1
>
> ## create a function -- junk2 -- that produces logistic growth
> junk2 <- mdlChooser("two")
> junk2
> res2 <- junk2(t,500,0.2,1000)
> res2
>


Try this:

mdlChooser <- function(type = c("one", "two")) {
   one <- function(x,N0,r) N0*exp(x*r)
   two <- function(x,N0,r,K) (N0*K)/(N0+(K-N0)*exp(-x*r))
   type <- match.arg(type)
   get(type)
}