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

[William Dunlap]

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


On Thu, Apr 16, 2020 at 7:25 AM Sokol Serguei <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(s) || is.call(s) && s[[1]]==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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