R help - Mar 2025 - [External] Creating model formulas programmatically

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 3:12?PM Richard M. Heiberger <rmh at 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 at
gmail.com> wrote:
> >
> > somenames <- c("Heigh", "Ho",
"Silver", "Away")
>
>
>
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The general formula is y ~ a + b + c + ...

There is this approach:
formula <- reformulate(independent_vars, response = "y")
model <- lm(formula, data = mydata)
summary(model)

It does not generate a string object, but the formula is still a string even if
it is of class formula. Also, in this approach you only get + and if you want
interactions or such you will need to code them into independent_vars.

This technically satisfies the parameters as I understand them, but it is
unsatisfying to me because it is playing with semantics. If I cannot generate a
string (no matter what you call it) then I cannot get to y ~ a + b + c + ...and
without that I do not have a model.

An alternative: Someone could write a function. Say I am using lm() so the
function will take a vector, a data frame, and a symbol. It will put them
together (as a black box) and spit out the answer. You will never see the
string, so it satisfies that requirement. However, it will generate a string
internally to make everything work. Again, playing with semantics.

I suggest that as stated the problem does not have a solution in a meaningful
way. The best I can do is to try to hide the string from you.


Tim

-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of Bert Gunter
Sent: Saturday, March 29, 2025 6:40 PM
To: Richard M. Heiberger <rmh at temple.edu>; R-help <R-help at
r-project.org>
Subject: Re: [R] [External] Creating model formulas programmatically

[External Email]

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 3:12?PM Richard M. Heiberger <rmh at 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 at
gmail.com> wrote:
> >
> > somenames <- c("Heigh", "Ho",
"Silver", "Away")
>
>
>
        [[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide https://www.r-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

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 at 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 3:12?PM Richard M. Heiberger <rmh at
temple.edu<mailto:rmh at 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 at
gmail.com<mailto:bgunter.4567 at gmail.com>> wrote:
>
> somenames <- c("Heigh", "Ho", "Silver",
"Away")


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