[Rd] advice on arguments

[Gabor Grothendieck]

Here is an approach.  fn.dots takes a character string, fn.name, such as
a function name and a named list, dots.  If fn.name is "f", say, then
it returns all components of dots whose name is of the form f.somestring
removing the f. prefix as well as components containing unprefixed
strings. It would typically be used like this:

f.dots <- fn.dots("f", dots)
do.call("f", f.dots)

and the user can specify that x be passed to all functions by
naming it x, to just f by naming it f.x.  If both x and f.x appears
then f.x takes precedence in a call to f.

fn.dots <- function(fn.name, dots) {
	pat <- paste("^", fn.name, "[.]", sep = "")
	nm <- names(dots)
	fn.nm <- grep(pat, nm, value = TRUE)
	dots[sub(pat, "", fn.nm)] <- dots[fn.nm]
	dots[grep("^[^.]*[.]", nm, value = TRUE)] <- NULL
	dots
}


dots <- list(a = 33, f.a = 55, g.a = 44, b = 56, g.c = 99)
fn.dots("f", dots) # list(a = 55, b = 56)
fn.dots("g", dots) # list(a = 44, b = 56, c = 99)
fn.dots("h", dots) # list(a = 33, b = 56)


On 6/29/06, Ben Bolker <bolker at zoo.ufl.edu> wrote:
>
>    I have a general style question about R coding.
>
>   Suppose I'm writing a function (foo1) that calls other functions
> (foo2, foo3, ...) which have complicated argument
> lists (e.g. optim(), plot()), _and_
> I may be calling several different functions in the body of
> foo1.  Since foo2 and foo3 have different sets of arguments, I
> can't just use "..." ; I did write some code a while ago that
> would look at formals() to dissect out arguments that should
> be passed to the different functions, but it seemed overly
> complex.
>
>  The particular case I have now is a little simpler.
>
>  foo2 (points3d) and foo3 (spheres3d)
> are both functions from the rgl package
> that pass arguments such as color, alpha, etc. along to
> an rgl.material() command with lots of possible arguments.
> (The function may also call segments3d or lines3d, but
> these all have the same arguments as points3d.)
> However, to change the size of points you use "size"; to
> change the size of spheres you use "radius".  Do I
> (1) add "radius" to the argument list, cluttering up
> the argument list for one particular special case?
> (2) add "size" to the argument list, so that it doesn't
> become part of "..." and I can say spheres3d(radius=size,...) ?
> (3) do something like
>    dotlist = list(...)
>    if (type=="s" && !is.null(dotlist$size)) radius <- dotlist$size
> and pull "size" out of ... myself (and make a note to that
> effect in  the documentation)?
>  (I guess another general solution to this is to ask for
> lists of arguments, like MoreArgs in mapply(). Another
> would be to go back and change spheres3d to make size
> a synonym for radius ... )
>
>  any thoughts?
>    Ben Bolker
>
>
> --
> 620B Bartram Hall                            bolker at zoo.ufl.edu
> Zoology Department, University of Florida    http://www.zoo.ufl.edu/bolker
> Box 118525                                   (ph)  352-392-5697
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>
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