formula mungeing

I can't compete with Gabor's "elegant" solution, but I don't understand why
your original "ugly" approach doesn't work.

g <- function(lambdas, f){
   z <- as.character(f)
   for(i in seq_along(lambdas))
      z[3]<-  sub(paste0("lambdas[", i, "]"), lambdas[i], z[3], fixed =
TRUE)
    formula(paste0(z[c(2,1,3)], collapse = " "))
}

f <- y ~ qss(x, lambda = lambdas[1]) + qss(z, lambdas[2]) + s
g(1:2, f)

y ~ qss(x, lambda = 1) + qss(z, 2) + s
<environment: 0x7f930e768598>

f <- y ~ qss(x, lambda = lambdas[1]) + qss(z, lambdas[2]) +

+     qss(z,lambdas[3]) + s

g(3:1, f)

y ~ qss(x, lambda = 3) + qss(z, 2) + qss(z, 1) + s
<environment: 0x7f930e7404f0>

Is there maybe a problem with the environment of the created formula? Or
have I misunderstood what you wanted?

Cheers,
Bert

Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Oct 23, 2020 at 6:33 AM Koenker, Roger W <rkoenker at 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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