Option 1)
vec <- c("a", "b")
combinations <- sapply(2:length(vec), function(x) apply(combn(vec, x), 2,
paste, collapse = ":"))
vec <- c(vec, unlist(combinations))
vec
option 2) generate the interaction terms in the data frame with the data and
then read the column names to get the new vector of variables. An interaction
term is just multiplying the values of each variable. The analysis can do that,
or you can do that. A complex answer is use base R, or use dplyr.
Base R only)
df <- data.frame(a = 1:5, b = 6:10, c = 11:15)
combinations <- combn(names(df), 2)
for (i in 1:ncol(combinations)) {
col1 <- combinations[1, i]
col2 <- combinations[2, i]
df[[paste(col1, col2, sep = ":")]] <- df[[col1]] * df[[col2]]
}
df
I can avoid paste in this alternative. I have tried to get closer to the
programming goal, but sacrificed ease of interpretation in the output:
df <- data.frame(a = 1:5, b = 6:10, c = 11:15)
combinations <- combn(names(df), 2)
for (i in seq_len(ncol(combinations))) {
df[[sprintf("col%d", i)]] <- df[[combinations[1, i]]] * df[[combinations[2,
i]]]
}
df
Using dplyr)
library(dplyr)
df <- data.frame(a = 1:5, b = 6:10, c = 11:15)
combinations <- combn(names(df), 2, simplify = FALSE)
df <- df %>%
mutate(across(all_of(combinations), ~ .[[1]] * .[[2]], .names =
"{.col[[1]]}:{.col[[2]]}"))
df
At the end, use colnames() for the vector of independent variables. Rejoin the
dependent variable to the data frame. Pass that to reformulate.
Tim
-----Original Message-----
From: Rui Barradas <ruipbarra...@sapo.pt>
Sent: Sunday, March 30, 2025 4:05 AM
To: Ebert,Timothy Aaron <teb...@ufl.edu>; Bert Gunter <bgunter.4...@gmail.com>;
Richard M. Heiberger <r...@temple.edu>; R-help <R-help@r-project.org>
Subject: Re: [R] [External] Creating model formulas programmatically
[External Email]
Hello,
I thought of answering "reformulate can solve the problem" but how do you
create quadratic terms with reformulate?
~(Heigh + Ho + Silver + Away)^2
is still a problem with no solution that I know of but paste/as.formula.
Or Bert's bquote or substitute.
Rui Barradas
Às 23:18 de 29/03/2025, Ebert,Timothy Aaron escreveu:
> 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-boun...@r-project.org> On Behalf Of Bert Gunter
> Sent: Saturday, March 29, 2025 6:40 PM
> To: Richard M. Heiberger <r...@temple.edu>; R-help
> <R-help@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 <r...@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.4...@gmail.com> wrote:
>>>
>>> somenames <- c("Heigh", "Ho", "Silver", "Away")
>>
>>
>>
>
> [[alternative HTML version deleted]]
>
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