[Rd] Augment base::replace(x, list, value) to allow list= to be a predicate?

[Gabor Grothendieck]

This is getting way off topic. I wasn't suggesting that gsubfn, which
does a lot more than this simple
example, as the implementation.

I was pointing out that the replace function idea can be extended to
sub and gsub and showing what
it would do.

On Tue, Mar 7, 2023 at 9:41 PM Steve Martin <stevemartin041 using gmail.com> wrote:
>
> That's an interesting example, as it's conceptually similar to what
> Pavel is proposing, but structurally different. gsubfn() is more
> complicated than a simple switch in the body of the function, and
> wouldn't work well as an anonymous function.
>
> Multiple dispatch can nicely encompass both of these cases. For replace(),
>
> library(S7)
>
> replace <- new_generic("replace", c("x", "list"), function(x, list,
> values, ...) {
>   S7_dispatch()
> })
>
> method(replace, list(class_any, class_any)) <- base::replace
>
> method(replace, list(class_any, class_function)) <- function(x, list,
> values, ...) {
>   replace(x, list(x, ...), values)
> }
>
> x <- c(1 ,2, NA, 3)
> replace(x, is.na(x), 0)
> [1] 1 2 0 3
>
> replace(x, is.na, 0)
> [1] 1 2 0 3
>
> And for gsub(),
>
> gsub <- new_generic("gsub", c("pattern", "replacement"),
> function(pattern, replacement, x, ...) {
>   S7_dispatch()
> })
>
> method(gsub, list(class_character, class_character)) <- base::gsub
>
> # My quick-and-dirty implementation as an example
> method(gsub, list(class_character, class_function)) <-
> function(pattern, replacement, x) {
>   m <- regexpr(pattern, x)
>   res <- replacement(regmatches(x, m))
>   mapply(gsub, pattern, as.character(res), x, USE.NAMES = FALSE)
> }
>
> gsub("^..", toupper, c("abc", "xyz"))
> [1] "ABc" "XYz"
>
> But this isn't a simple change to replace() anymore, and I may just be
> spending too much time tinkering with Julia.
>
> Steve
>
> On Tue, 7 Mar 2023 at 07:34, Gabor Grothendieck <ggrothendieck using gmail.com> wrote:
> >
> > This could be extended to sub and gsub as well which gsubfn in the
> > gusbfn package already does:
> >
> >   library(gsubfn)
> >   gsubfn("^..", toupper, c("abc", "xyz"))
> >   ## [1] "ABc" "XYz"
> >
> > On Fri, Mar 3, 2023 at 7:22 PM Pavel Krivitsky <p.krivitsky using unsw.edu.au> wrote:
> > >
> > > Dear All,
> > >
> > > Currently, list= in base::replace(x, list, value) has to be an index
> > > vector. For me, at least, the most common use case is for list= to be
> > > some simple property of elements of x, e.g.,
> > >
> > > x <- c(1,2,NA,3)
> > > replace(x, is.na(x), 0)
> > >
> > > Particularly when using R pipes, which don't allow multiple
> > > substitutions, it would simplify many of such cases if list= could be a
> > > function that returns an index, e.g.,
> > >
> > > replace <- function (x, list, values, ...) {
> > >   # Here, list() refers to the argument, not the built-in.
> > >   if(is.function(list)) list <- list(x, ...)
> > >   x[list] <- values
> > >   x
> > > }
> > >
> > > Then, the following is possible:
> > >
> > > c(1,2,NA,3) |> replace(is.na, 0)
> > >
> > >                         Any thoughts?
> > >                         Pavel
> > > ______________________________________________
> > > R-devel using r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
> >
> >
> > --
> > Statistics & Software Consulting
> > GKX Group, GKX Associates Inc.
> > tel: 1-877-GKX-GROUP
> > email: ggrothendieck at gmail.com
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel



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