>>>>> Winston Chang <winstoncha...@gmail.com>
>>>>> on Fri, 23 Jan 2015 10:15:53 -0600 writes:
> I think you can simplify a little by replacing this:
> pkg %in% loadedNamespaces()
> with this:
> .getNamespace(pkg)
almost: It would be
!is.null(.getNamespace(pkg))
> Whereas getNamespace(pkg) will load the package if it's not already
> loaded, calling .getNamespace(pkg) (note the leading dot) won't load
> the package.
indeed.
And you, Winston, are right that this new code snippet would be
an order of magnitude faster :
##-----------------------------------------------------------------------------
f1 <- function(pkg) pkg %in% loadedNamespaces()
f2 <- function(pkg) !is.null(.getNamespace(pkg))
require(microbenchmark)
pkg <- "foo"; (mbM <- microbenchmark(r1 <- f1(pkg), r2 <- f2(pkg)));
stopifnot(identical(r1,r2)); r1
## Unit: microseconds
## expr min lq mean median uq max neval cld
## r1 <- f1(pkg) 38.516 40.9790 42.35037 41.7245 42.4060 82.922 100 b
## r2 <- f2(pkg) 1.331 1.8285 2.13874 2.0855 2.3365 7.252 100 a
## [1] FALSE
pkg <- "stats"; (mbM <- microbenchmark(r1 <- f1(pkg), r2 <- f2(pkg)));
stopifnot(identical(r1,r2)); r1
## Unit: microseconds
## expr min lq mean median uq max neval cld
## r1 <- f1(pkg) 29.955 31.2575 32.27748 31.6035 32.1215 62.428 100 b
## r2 <- f2(pkg) 1.067 1.4315 1.71437 1.6335 1.8460 9.169 100 a
## [1] TRUE
loadNamespace("Matrix")
## <environment: namespace:Matrix>
pkg <- "Matrix"; (mbM <- microbenchmark(r1 <- f1(pkg), r2 <- f2(pkg)));
stopifnot(identical(r1,r2)); r1
## Unit: microseconds
## expr min lq mean median uq max neval cld
## r1 <- f1(pkg) 32.721 33.5205 35.17450 33.9505 34.6050 65.373 100 b
## r2 <- f2(pkg) 1.010 1.3750 1.93671 1.5615 1.7795 12.128 100 a
## [1] TRUE
##-----------------------------------------------------------------------------
Hence, indeed,
!is.null(.getNamespace(pkg))
seems equivalent to
pkg %in% loadedNamespaces()
--- when 'pkg' is of length 1 (!!!)
but is 20 times faster.... and we have
11 occurrences of ' <...> %in% loadedNamespaces() '
in the "base packages" in the R (devel) sources,
3 in base, 2 in methods, 3 in stats, 2 in tools, 1 in utils..
On the other hand,
pkg %in% loadedNamespaces()
is extremely nicely readable code, whereas
!is.null(.getNamespace(pkg))
is pretty much the contrary.
.. and well readable code is so much easier to maintain etc,
such that in many cases, code optimization with the cost of
code obfuscation is *not* desirable.
Of course we could yet again use a few lines of C and R code to
provide a new R lowlevel function, say
is.loadedNamespace()
which would be even faster than !is.null(.getNamespace(pkg))
...
...
but do we have *any* evidence that this would noticably speedup
any higher level function such as library() ?
Thank you, again, Winston; you've opened an interesting topic!
--
Martin Maechler, ETH Zurich
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
