Gabor Grothendieck wrote:
>
> I've provided an argument against it and no one has provided one
> for it. The so-called identical code Ivo showed was not identical
> and, in fact, was flawed.
no, you're wrong. you think of the part where ivo shows what he'd like
to have; the example i was referring to was almost identical with
yours, except for the explicit return and '=' used for assignment.
> Your first/last example could be
> written:
>
> f <- function() letters
> L <- structure(f()[1:2], names = c("first", "last"))
>
indeed, but:
- this still does not allow one to use the names directly, only as
L$first etc., with the syntactic and semantic (longer lookup times) penalty;
- using structure you add yet another source of performance penalty; a
quick naive benchmark hints that it doubles the time elapsed if the
returned list is inaccessible otherwise, and adds one order of magnitude
if the list has to be copied:
f1= function() as.list(letters)
f2 =local({ letters = as.list(letters); function() letters })
source('http://rbenchmark.googlecode.com/svn/trunk/benchmark.r')
benchmark(replications=10000, columns=c('test', 'elapsed'),
'f1 direct'=f1(),
'f1 structure'=structure(f1(), names=letters),
'f2 direct'=f2(),
'f2 structure'=structure(f2(), names=letters))
# test elapsed
# 1 f1 direct 0.171
# 2 f1 structure 0.693
# 3 f2 direct 0.048
# 4 f2 structure 0.594
instead of a syntactically (and semantically, if done appropriately)
clean solution:
c(a, b) = f()[1,3]
# work with a and b
you offer a glut:
l = structure(f()[1,3], names=c('a', 'b'))
# work with l$a and l$b
> or one could define a function to do that without having
> to modify the language. Given the relative infrequency
> of this it hardly seems to merit a language feature.
>
infrequency of what? of people's inventing ugly hacks to get arround
the inability to capture multiple return values directly? sure, this is
a good argument against having someone do the job, but is it a good
argument against having the feature in the language?
vQ
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
