[R] Model Formulae Evaluation

[Gabor Grothendieck]

On Mon, Jun 20, 2011 at 9:08 AM, albeam <beam.andrew at gmail.com> wrote:
> Please allow me to clarify my original question. What I really need to be
> able to do it is to take arbitrary functions and evaluate them for arbitrary
> parameter values. I'm doing the optimization myself, so I need to be able to
> take a user's function and evaluate them at the current parameter values
> during my optimization process. So it would look something like this:
>
> opt.fun <- function(user.formula, param.values)
> {
>    #--- I would do some optimization here ---#
>
>    fitted.values <- eval.fun(user.formula, param.values) ##<---- this is
> what I need
> }
>
> Where fitted.values is a vector of the same size as the x-values in
> user.formula. nls() does this somehow. I could do this easily myself if I
> have the user pass the formula in reverse polish notation, but I was hoping
> there was a more canonical was to do this in R.

fn in gsubfn, when used to preface a function like this, will convert
certain formula arguments to functions.  Here we preface the identity
function so that we just get back the converted argument directly:

> library(subfn)
> fo <- ~ x + 1 # or fo <- x ~ x + 1
> fn$identity(fo)
function (x)
x + 1

See
http://gsubfn.googlecode.com
?fn
vignette("gsubfn")

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