Creating model formulas programmatically

Gabor, Duncan, et. al.

1. Thank you for your great comments and solutions. This is what I was
hoping for!

2. Duncan: I completely agree with your criticisms. In fact, I realized the
for() loop only needed the <- assignment, but your comment is important to
note. However, I didn't like the for() loop either; I *much* preferred your
Reduce() solution which is exactly the sort of elegant functionally based
solution that R excels at. I am glad that you put it into the record.

3. If I may indulge those who are following this thread, yet another simple
approach that just uses call() recursively is:

recurseCall <- function(nms, FUN = '+')
{
    if(length(nms) > 2) call(FUN, nms[[1]], Recall(nms[-1]))
    else call(FUN, nms[[1]],nms[[2]])
}
## yielding

recurseCall(nms)

Heigh + (Ho + (Silver + Away))

While this result is different than that given by the others, it is
syntactically equivalent and yields identical results when used.
However, Duncan's Reduce() solution seems to me "obviously" better. In
fact, I think recurseCall just recapitulates the logic of Reduce().

4. And, again, I realize that versions of str2lang(paste(somename, collapse
= ' + ')) work just fine, but I was explicitly interested in eliciting the
bushel basket of elegant (imo) approaches that have been offered.

Again, my thanks to all.

Bert








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



On Sun, Mar 30, 2025 at 6:11?AM Gabor Grothendieck <ggrothendieck at gmail.com>
wrote:

Another solution.  reformulate + substitute + as.formula:

substitute(~ (.)^2, list(. = reformulate(somenames)[[2]])) |> as.formula()

On Sat, Mar 29, 2025 at 5:31?PM Bert Gunter <bgunter.4567 at gmail.com>
wrote:

Note: I am almost certain that this has been asked and answered here
before, so my apologies for the redundant query.

I also know that there are several packages that will do this, but I wish
to do it using base R functions only (see below).

The query: Suppose I have a character vector of names like this:
somenames <- c("Heigh", "Ho", "Silver", "Away")
(maybe dozens or hundreds: i.e. lots of names)

Now suppose want to put these in a model formula like this:
~ (Heigh + Ho + Silver + Away)^2

... But **without** pasting them into a character vector and using
parse(text = ...) , which, I grant, is sometimes the simplest way.
Instead, I want to do it using Base R's computing on the language
functions. I can do this with bquote() or substitute(), for example, like
this:

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

## yielding

form

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

My question: Is there a simpler/slicker way to do this? This seems kinda
kludgy, and I have the feeling that I'm missing something obviously

better

(in base R only; obviously better stuff is in various packages)

Best to all,
Bert

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

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