[R] [External] Creating model formulas programmatically

[Bert Gunter]

As always, I would like to thank all who responded for their insights and
suggestions. I have learned from them.

Thus far, my own aesthetic preference -- and therefore not to be considered
in any sense as a "best" approach -- is to use Duncan's suggestion to
produce the call directly with call() rather than substitute in my simple
for() loop; i.e.

somenames <- c("Heigh", "Ho", "Silver", "Away")
nms <- lapply(somenames, as.name)
frm<- nms[[1]]
for(x in nms[-1]) frm <<- call("+", frm, x)
frm <-bquote(~ (.(frm))^2, list(frm =frm))

## which yields

> frm
~(Heigh + Ho + Silver + Away)^2

I obviously still did not make make my requirements clear, since after
converting the character string names into language onjects via as.name(),
the above (and Duncan's response and my original query) do not make any use
of string parsing/conversion. That is what I meant. As respondents pointed
out, there are some base R functions that put the string manipulations
behind a curtain so that one need not directly worry about them, but I
didn't want to go there either. Again, my apologies for my imprecision.

Finally, I still welcome any other approaches along these lines and
especially would appreciate anyone pointing out any fatal flaws or even
modest infelicities in the above approach.

Cheers,
Bert

"An educated person is one who can entertain new ideas, entertain others,
and entertain herself."



On Sat, Mar 29, 2025 at 6:32 PM Ebert,Timothy Aaron <tebert using ufl.edu> wrote:

> I am confused. Richard's answer that Bert did not like did not use parse
> explicitly. Richard pasted together a string that a function like lm() will
> have to parse to run the analysis. However, the answers so far do not use
> parse(). In the reply to Richard, Bert indicated we cannot use strings.
> Even if I pass a vector where R can assume that the first variable is the
> dependent variable and all others are independent variables, I see no way
> of processing that within the current modeling system without generating a
> formula (a string) that gets parsed.
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Richard M.
> Heiberger
> Sent: Saturday, March 29, 2025 8:47 PM
> To: Bert Gunter <bgunter.4567 using gmail.com>
> Cc: R-help <R-help using r-project.org>
> Subject: Re: [R] [External] Creating model formulas programmatically
>
> [External Email]
>
> my take of the assignment was to avoid 'parse' specifically.
> we start with a character vector, so avoiding characters is not possible.
> i was dealing with the fortune "if parse is the answer, you have the wrong
> question"
>
> Sent from my iPhone
>
> On Mar 29, 2025, at 15:39, Bert Gunter <bgunter.4567 using gmail.com> wrote:
>
> 
> Thanks, Rich.
>
> I thought of that, too, but it violates the spirit of my restraints (to
> avoid character strings), which I unfortunately did not clearly articulate.
> So my apologies for that failure. My concern is that with more complex
> model formula, using as.formula, etc. to parse/convert character strings
> can get a bit hairy. But in most cases, as here maybe, it may be perfectly
> fine. So think of my post as mostly my attempt to learn some new tricks
> rather than to solve a useful problem. I hope this is not unfair to the
> list.
>
> Cheers,
> Bert
>
>
>
>
>
> On Sat, Mar 29, 2025 at 3:1 PM Richard M. Heiberger <rmh using temple.edu
> <mailto:rmh using temple.edu>> wrote:
> > somenames <- c("Heigh", "Ho", "Silver", "Away")
> > as.formula(paste("~(",paste(somenames, collapse="+"),")^2"))
> ~(Heigh + Ho + Silver + Away)^2
> >
>
> > On Mar 29, 2025, at 14:30, Bert Gunter <bgunter.4567 using gmail.com<mailto:
> bgunter.4567 using gmail.com>> wrote:
> >
> > somenames <- c("Heigh", "Ho", "Silver", "Away")
>
>
>
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>
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