[R] Creating model formulas programmatically

[Duncan Murdoch]

Your approach seems reasonable to me, though I wouldn't do it that way.

The way I work this sort of thing out is to get R to do a simple 
example, then see what it did, and duplicate that.

For example,

   f <-  ~ (Heigh + Ho + Silver + Away)^2

Then look at as.list(f), as.list(f[[2]]), as.list(f[[c(2,2)]]), etc., 
and reproduce that structure.

So I can reproduce that with

   f <- ~(Heigh)^2
   f[[c(2,2,2)]] <- call("+", f[[c(2,2,2)]], as.name("Ho"))
   f[[c(2,2,2)]] <- call("+", f[[c(2,2,2)]], as.name("Silver"))
   f[[c(2,2,2)]] <- call("+", f[[c(2,2,2)]], as.name("Away"))

and there are obvious ways to convert that to work with names in a vector.

Duncan Murdoch

On 2025-03-29 5:30 p.m., Bert Gunter 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."
> 
> 	[[alternative HTML version deleted]]
> 
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