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

[Simon Urbanek]

Sergei,

the main problem that I was pointing out is is that there is no way you can introduce the new syntax without breaking the old one. The expression is evaluated to obtain a function, so by definition using anything that results in a valid expression for your syntax will break. E.g., using sapply(x, (foo)) is completely valid so you can't just change the evaluation of the expression to something different (which is what you're doing). As people were pointing out there are many ways to do this if you change the syntax.

I'm not arguing against the principle, I'm arguing about your particular proposal as it is inconsistent and not general. 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 <sokol using 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 <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. 
>> 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. ______________________________________________ R-devel using r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel 
>> 
>