[Rd] good practice for values not provided

[Gabor Grothendieck]

One possibility is:

f <- function(a, b, x) if (missing(x)) a+b else a-b-x

although that does have the disadvantage that one cannot explicitly tell
it not to use x but rather its denoted by its absence.

On 11/19/06, Tamas K Papp <tpapp at princeton.edu> wrote:
> Hi,
>
> I am writing a collection of functions which I plan to share as a
> package later (when they are tested thoroughly), so I would like to do
> things "right" from the beginning...
>
> I encountered a minor question of style.  Consider a function
>
> f <- function(a,b,x=NULL) {
>  ## ...
> }
>
> if !is.null(x), f will use x to calculate the result, but if
> is.null(x), it will do something else not involving x at all (using
> any x would be meaningless here, so I can't use
> x=calcsomethingfrom(a,b)).
>
> What's the accepted way of indicating this in R with a default for x?
> x=FALSE? x=NA? x=NULL?
>
> Thanks,
>
> Tamas
>
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