Le 19/04/2020 à 20:46, Gabor Grothendieck a écrit :
You can get pretty close to that already using fn$ in the gsubfn package:
library(gsubfn) fn$sapply(split(mtcars, mtcars$cyl), x ~
summary(lm(mpg ~ wt, x))$r.squared)
4 6 8 0.5086326 0.4645102 0.4229655
Right, I thought about similar syntax but this implementation has
similar flaws pointed by Simon, i.e. it reduces the domain of valid
inputs (though not on the same parameters). Take an example:
library(gsubfn)
fn$sapply(quote(x+y), as.character)
#Error in lapply(X = X, FUN = FUN, ...) : object 'x' not found
while
sapply(quote(x+y), as.character)
#[1] "+" "x" "y"
This makes me think that it could be advantageous to replace
match.fun(FUN) in *apply() family by as.function(FUN) with obvious
additional methods:
as.function.character <- function(x) match.fun(x)
as.function.name <- function(x) match.fun(x)
Such replacement would leave current usage of *apply() as is but at the
same time would leave enough space for users who want to adapt *apply()
to their objects like formula or whatever class that is currently not
convertible to functions by match.fun()
Would it be possible?
Best,
Serguei.
It is not specific to sapply but rather fn$ can preface most
functions. If the only free variables are the arguments to the
function then you can omit the left hand side of the formula, i.e. the
arguments to the function are implied by the free variables in the
right hand side. Here x is the implied argument to the function
because it is a free variable. We did not have use the name x. Any
name could be used. It is the fact that it is a free variable, not its
name, that matters.
fn$sapply(split(mtcars, mtcars$cyl), ~ sum(dim(x)))
4 6 8 22 18 25 On Fri, Apr 17, 2020 at 4:11 AM Sokol Serguei
<so...@insa-toulouse.fr> wrote:
Thanks Simon, Now, I see better your argument. Le 16/04/2020 à 22:48,
Simon Urbanek a écrit :
... I'm not arguing against the principle, I'm arguing about your
particular proposal as it is inconsistent and not general.
This sounds promising for me. May be in a (new?) future, R core will
come with a correct proposal for this principle? Meanwhile, to avoid
substitute(), I'll look on the side of formula syntax deviation as
your example x ~> i + x suggested. Best, Serguei.
Personally, I find the current syntax much clearer and readable
(defining anything by convention like . being the function variable
seems arbitrary and "dirty" to me), but if you wanted to define a
shorter syntax, you could use something like x ~> i + x. That said,
I really don't see the value of not using function(x) [especially
these days when people are arguing for long variable names with the
justification that IDEs do all the work anyway], but as I said, my
argument was against the actual proposal, not general ideas about
syntax improvement. Cheers, Simon
On 17/04/2020, at 3:53 AM, Sokol Serguei <so...@insa-toulouse.fr>
wrote: Simon, Thanks for replying. In what follows I won't try to
argue (I understood that you find this a bad idea) but I would like
to make clearer some of your point for me (and may be for others).
Le 16/04/2020 à 16:48, Simon Urbanek a écrit :
Serguei,
On 17/04/2020, at 2:24 AM, Sokol Serguei <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.
It's not in any way "neater", not only is it less readable, it's
just plain wrong. What if the expression returned a function?
do you mean like in l=sapply(1:3, function(i) function(x) i+x)
l[[1]](3) # 4 l[[2]](3) # 5 This is indeed a corner case but a pair
of () or {} can keep wsapply() in course: l=wsapply(1:3,
(function(x) .+x)) l[[1]](3) # 4 l[[2]](3) # 5
How do you know that you don't want to apply the result of the call?
A small example (if it is significantly different from the one
above) would be very helpful for me to understand this point.
For the same reason the implementation below won't work - very
often you just pass a symbol that evaluates to a function and
always en expression that returns a function and there is no way
to distinguish that from your new proposed syntax.
Even with () or {} around such "dotted" expression? Best, Serguei.
When you feel compelled to use substitute() you should hear alarm
bells that something is wrong ;). You can certainly write a new
function that uses a different syntax (and I'm sure someone has
already done that in the package space), but what you propose is
incompatible with *apply in R (and very much not R syntax).
Cheers, Simon
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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