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

[Sokol Serguei]

Thanks Henrik,

Probably, it will be the solution I'll retain.

Best,
Serguei.

Le 16/04/2020 à 18:50, Henrik Bengtsson a écrit :

I'm sure this exists elsewhere, but, as a trade-off, could you achieve
what you want with a separate helper function F(expr) that constructs
the function you want to pass to [lsv]apply()?  Something that would
allow you to write:

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

Such an F() function would apply elsewhere too.

/Henrik

On Thu, Apr 16, 2020 at 9:30 AM Michael Mahoney
<mike.mahoney....@gmail.com> wrote:

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 <so...@insa-toulouse.fr>
Date: Thu, Apr 16, 2020 at 12:03 PM
Subject: Re: [Rd] suggestion: "." in [lsv]apply()
To: William Dunlap <wdun...@tibco.com>
Cc: r-devel <r-devel@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 <so...@insa-toulouse.fr
<mailto:so...@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.

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