[R] formula mungeing

[Koenker, Roger W]

Thanks, Gabor!  Very elegant!

> On Oct 23, 2020, at 4:15 PM, Gabor Grothendieck <ggrothendieck using gmail.com> wrote:
> 
> 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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> 
> 
> 
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