[Rd] suggestion: "." in [lsv]apply()

[Michael Mahoney]

This syntax is already implemented in the {purrr} package, more or
less -- you need to add a tilde before your function call for it to
work exactly as written:

purrr::map_dbl(split(mtcars, mtcars$cyl), ~ summary(lm(wt ~ mpg, .))$r.squared)

is equivalent to

sapply(split(mtcars, mtcars$cyl), function(d) summary(lm(mpg ~ wt,
d))$r.squared)

Seems like using this package is probably an easier solution for this
wish than adding a reserved variable and adding additional syntax to
the apply family as a whole.

Thanks,

-Mike

> From: Sokol Serguei <sokol using insa-toulouse.fr>
> Date: Thu, Apr 16, 2020 at 12:03 PM
> Subject: Re: [Rd] suggestion: "." in [lsv]apply()
> To: William Dunlap <wdunlap using tibco.com>
> Cc: r-devel <r-devel using r-project.org>
>
>
> Thanks Bill,
>
> Clearly, my first proposition for wsapply() is quick and dirty one.
> However, if "." becomes a reserved variable with this new syntax,
> wsapply() can be fixed (at least for your example and alike) as:
>
> wsapply=function(l, fun, ...) {
>      .=substitute(fun)
>      if (is.name(.) || is.call(.) && .[[1]]==as.name("function")) {
>          sapply(l, fun, ...)
>      } else {
>          sapply(l, function(d) eval(., list(.=d)), ...)
>      }
> }
>
> Will it do the job?
>
> Best,
> Serguei.
>
> Le 16/04/2020 à 17:07, William Dunlap a écrit :
> > Passing in a function passes not only an argument list but also an
> > environment from which to get free variables. Since your function
> > doesn't pay attention to the environment you get things like the
> > following.
> >
> > > wsapply(list(1,2:3), paste(., ":", deparse(s)))
> > [[1]]
> > [1] "1 : paste(., \":\", deparse(s))"
> >
> > [[2]]
> > [1] "2 : paste(., \":\", deparse(s))" "3 : paste(., \":\", deparse(s))"
> >
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com <http://tibco.com>
> >
> >
> > On Thu, Apr 16, 2020 at 7:25 AM Sokol Serguei <sokol using insa-toulouse.fr
> > <mailto:sokol using insa-toulouse.fr>> wrote:
> >
> >     Hi,
> >
> >     I would like to make a suggestion for a small syntactic
> >     modification of
> >     FUN argument in the family of functions [lsv]apply(). The idea is to
> >     allow one-liner expressions without typing "function(item) {...}" to
> >     surround them. The argument to the anonymous function is simply
> >     referred
> >     as ".". Let take an example. With this new feature, the following call
> >
> >     sapply(split(mtcars, mtcars$cyl), function(d) summary(lm(mpg ~ wt,
> >     d))$r.squared)
> >     #        4         6         8
> >     #0.5086326 0.4645102 0.4229655
> >
> >
> >     could be rewritten as
> >
> >     sapply(split(mtcars, mtcars$cyl), summary(lm(mpg ~ wt, .))$r.squared)
> >
> >     "Not a big saving in typing" you can say but multiplied by the
> >     number of
> >     [lsv]apply usage and a neater look, I think, the idea merits to be
> >     considered.
> >     To illustrate a possible implementation, I propose a wrapper
> >     example for
> >     sapply():
> >
> >     wsapply=function(l, fun, ...) {
> >          s=substitute(fun)
> >          if (is.name <http://is.name>(s) || is.call(s) &&
> >     s[[1]]==as.name <http://as.name>("function")) {
> >              sapply(l, fun, ...) # legacy call
> >          } else {
> >              sapply(l, function(d) eval(s, list(.=d)), ...)
> >          }
> >     }
> >
> >     Now, we can do:
> >
> >     wsapply(split(mtcars, mtcars$cyl), summary(lm(mpg ~ wt, .))$r.squared)
> >
> >     or, traditional way:
> >
> >     wsapply(split(mtcars, mtcars$cyl), function(d) summary(lm(mpg ~ wt,
> >     d))$r.squared)
> >
> >     the both work.
> >
> >     How do you feel about that?
> >
> >     Best,
> >     Serguei.
> >
> >     ______________________________________________
> >     R-devel using r-project.org <mailto:R-devel using r-project.org> mailing list
> >     https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
>
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