[R] formula mungeing

[Gabor Grothendieck]

Recursively walk the formula performing the replacement:

g <- function(e, ...) {
    if (length(e) > 1) {
        if (identical(e[[2]], as.name(names(list(...))))) {
          e <- eval(e, list(...))
        }
        if (length(e) > 1) for (i in 1:length(e)) e[[i]] <- Recall(e[[i]], ...)
    }
    e
}

g(f, lambdas = 2:3)
## y ~ qss(x, lambda = 2L) + qss(z, 3L) + s

On Fri, Oct 23, 2020 at 9:33 AM Koenker, Roger W <rkoenker using illinois.edu> wrote:
>
> Suppose I have a formula like this:
>
>         f <- y ~ qss(x, lambda = lambdas[1]) + qss(z, lambdas[2]) + s
>
> I’d like a function, g(lambdas, f)  that would take g(c(2,3), f) and produce the new
> formula:
>
>         y ~ qss(x, lambda = 2) + qss(z, 3) + s
>
> For only two qss terms I have been using
>
>         g <- function(lambdas, f){
>                 F <- deparse(f)
>                 F <- gsub("lambdas\\[1\\]",lambdas[1],F)
>                 F <- gsub("lambdas\\[2\\]",lambdas[2],F)
>                 formula(F)
>         }
> but this is ugly and doesn’t extend nicely to more qss terms.  Isn’t there some
> bquote() magic that can be invoked?  Or something else entirely?
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