[R] Construct a function with argments specified by an R expression

[Gabor Grothendieck]

Here is an approach using as.function.formula from gsubfn:

library (gsubfn)

# inputs
arg_names <- head(letters)
f <- function() {}

formals(f) <- formals(as.function(reformulate(arg_names)))
f

On Sun, Oct 26, 2025 at 10:47 AM Gabor Grothendieck
<ggrothendieck using gmail.com> wrote:
>
> This can be simplified slightly to
>
>   # inputs
>   arg_names <- c("x", "y", paste0("a", 1:3), paste0("b", 1:3))
>   f <- function() {}
>
>   arg <- alist(x = )
>   formals(f) <- setNames(rep(arg, length(arg_names)), arg_names)
>   f
>
>   ## function (x, y, a1, a2, a3, b1, b2, b3)
>   ## {
>   ## }
>
> On Sun, Oct 26, 2025 at 10:41 AM Gabor Grothendieck
> <ggrothendieck using gmail.com> wrote:
> >
> > Define the names and a prototype and then use formals(f) <- ... as shown.
> >
> >   # inputs
> >   arg_names <- c("x", "y", paste0("a", 1:3), paste0("b", 1:3))
> >   f <- function() {}
> >
> >   arg <- alist(x = )
> >   formals(f) <- setNames(c(arg, rep(arg, length(arg_names)-1)), arg_names)
> >   f
> >
> > giving
> >
> >   function (x, y, a1, a2, a3, b1, b2, b3)
> >   {
> >   }
> >
> > On Fri, Oct 24, 2025 at 10:23 PM Rolf Turner <rolfturner using posteo.net> wrote:
> > >
> > >
> > > I want to build a function (say "buildFn") to *return* a function of the
> > > form
> > >
> > >     foo(x,y,a1, ... an, b1, ..., bn)
> > >
> > > where the arguments ai and bi are given in the form of a list created
> > > in R.  E.g. I'd like to be able to say
> > >
> > >      argnms <- c(paste0("a",1:3),paste0("b",1:3"))
> > >      foo <- buildFn(argnms)
> > >
> > > with the resulting "foo" having arguments x, y, a1, a2, a3, b1, b2, b3.
> > >
> > > I thought I might be able to do this using "formals<-" but I cannot get
> > > this to work.  i could provide more detail of what I've tried, but it's
> > > probably not worth it.
> > >
> > > Can anyone steer me in the right direction?  Thanks.
> > >
> > > cheers,
> > >
> > > Rolf Turner
> > >
> > > --
> > > Honorary Research Fellow
> > > Department of Statistics
> > > University of Auckland
> > > Stats. Dep't. (secretaries) phone:
> > >          +64-9-373-7599 ext. 89622
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> > >
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> > > PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
> > > and provide commented, minimal, self-contained, reproducible code.
> >
> >
> >
> > --
> > Statistics & Software Consulting
> > GKX Group, GKX Associates Inc.
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> > email: ggrothendieck at gmail.com
>
>
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com



-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com