[Rd] match.arg
Spencer Graves
spencer.graves@pdf.com
Mon Feb 24 17:56:05 2003
Thanks for your reply.
I'm trying to generalize the MASS function "stepAIC" to study the
effects of hierarchy for both interactions and parabolic terms. I
include a new argument 'hierarchy = c("include", "exclude", "ignore")'
being a 2-vector, with the first component for interaction and the
second for parabolic terms:
* "exclude" fails to consider A:B (or A^2) unless both A and B are
currently in the model. This is the current default for interactions
but not for parabolic terms.
* "include" forces A:B to be evaluated with 3 degrees of freedom if
neither A nor B are currently in the model, 2 degrees of freedom if only
1 are in the model, and 1 degree of freedom if both are currently in the
model (assuming A and B are both either numerical variables or 2-level
factors). George Box says he invented response surface methods for a
chemical plant that had only interactions. The plan had gone through
several general managers, who had done what they could with one factor
at a time experiments. I plan to analyze several Taguchi 3-level
experiments in order to evaluate effect sparcity and the frequency with
which both interactions and parabolic terms occur in industrial
experimentation, and I need an automated way of doing this.
* "ignore" means include or exclude the interaction independent of
whether the main effect is in the model. This is the current default
for A^2.
I want to make "include" the default for both A:B and A^2. In my
revision of stepAIC, I call match.arg as follows;
hierarchy <- rep(match.arg(hierarchy), length=2)
What do you think? I know that one example does not justify adding a
rarely used option to a general tool. However, it occurred to me that
there might be other applications
#################
Thanks for reminding me about the "seq(length= length(arg))"
construction. After I sent that email, I discovered that problem, and
added the following line right before the "for" loop:
if((length(arg)==length(choices)) && all(arg==choices))
return(choices[1])
Since I had heard no reply, I decided not to issue a "correction" to an
email that might go nowhere or might only irritate the recipients.
Thanks again for your comments and all your effort and creativity in the
R project.
Best Wishes,
Spencer Graves
Martin Maechler wrote:
>>>>>>"Spencer" == Spencer Graves <spencer.graves@pdf.com>
>>>>>> on Mon, 17 Feb 2003 17:43:23 -0800 writes:
>>>>>
>
> Spencer> Hello: I'm not on the "r-devel" list, but I just
> Spencer> modified "match.arg" from R 1.6.2 for Windows to
> Spencer> accept a vector for "arg".
>
> Spencer> Is it appropriate that I send such things to
> Spencer> this email address for consideration for inclusion
> Spencer> in a future release?
>
> yes (using "R-devel" for ...).
> But why is this current proposal really useful?
> Note that I can't see reason to match more than one argument to the
> *same* list of choices. `choices' already is a vector typically...
>
> Making a function more complicated makes it also more
> error-prone, so I think we'd need a good motivation for it.
> E.g., your proposal below quite badly fails when
> length(arg) == 0, since you've used the ``well-known to be unsafe''
> 1:length(arg) idiom instead of the safe seq(length= length(arg)) one.
>
> Regards,
> Martin
>
> Spencer> I just compared this with "match.arg" in
> Spencer> S-Plus 6.1 for Windows. There, I got the
> Spencer> following:
>
> >> match.arg(c("a","b"), c("aa", "bb"))
> Spencer> [1] "aa" "bb"
>
>
>
>
> Spencer> However, match.arg(c("a", "b")) in a test
> Spencer> function with "default" = c("aa", "bb") returned
> Spencer> only "a"; the following returns c("aa", "bb").
>
> Spencer> Thanks for all your hard work in developing this
> Spencer> marvelous product.
>
> Spencer> Sincerely, Spencer Graves
>
> match.arg <-
> function (arg, choices)
> {
> if (missing(choices)) {
> formal.args <- formals(sys.function(sys.parent()))
> choices <- eval(formal.args[[deparse(substitute(arg))]])
> }
> # cat("choices =", choices, "\n")
> for(j in 1:length(arg)){
> if (all(arg[j] == choices))
> arg[j] <- choices[1]
> else{
> i <- pmatch(arg[j], choices)
> if (is.na(i))
> stop(paste("ARG should be one of", paste(choices, collapse =
> ", "),
> sep = " "))
> if (length(i) > 1)
> stop("there is more than one match in match.arg")
> arg[j] <- choices[i]
> }
> }
> arg
> }