Martin Maechler wrote:
"CAPE" == Charles Annis, P E <charles.an...@statisticalengineering.com>
on Thu, 19 Mar 2009 22:46:10 -0400 writes:
>> ?is.na
>> x <- c(NA, 3, 4, 5, NA)
>> which(is.na(x))
CAPE> [1] 1 5
well, of course.
But note that which.na(.) could be implemented to be
faster (because needing much less memory) than the above,
notably when x is large and has only few NAs
But this now has *REALLY* changed into a topic belonging to
R-devel, not R-help
--> hence I've diverted the thread to there.
I have recently entertained similar thoughts, i.e. wished for R
functions that compute
which( function_returning_logical(..) )
and also
any( function_returning_logical(..) )
directly {on .Internal i.e. C-level} instead of going to
construct the potentially huge logical vector.
For what functions should this happen?
I agree that is.na() is one of them; but then, why not
is.nan() / is.finite()
too?
Instead of defining a slew of such functions
which.foo(), which.bar(), any.foo(), any.bar(), etc,
it would be nice to have a generic interface such as
whichApply(x, is.na)
whichApply(x, is.nan)
anyApply(x, is.na)
where internally, for some functions {in a given internal
table}, the fast shortcut would be used, and for others the
interface would be equivalent to which( thatFunction( x ) )
A couple of different interfaces to the same idea:
- which() could recognize a few thatFunction(x) calls before
evaluating them, and do the fast internal version. (This is hard
because it needs to know
that the user hasn't redefined is.na, etc. Probably not worth doing.)
- which() could gain a new arg, so that
which(x, test=is.na)
would do as your whichApply() does.
Duncan Murdoch
Martin Maechler, ETH Zurich (and R Core team)
CAPE> Charles Annis, P.E.
CAPE> charles.an...@statisticalengineering.com
CAPE> phone: 561-352-9699
CAPE> eFax: 614-455-3265
CAPE> http://www.StatisticalEngineering.com
CAPE> -----Original Message-----
CAPE> From: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org] On
CAPE> Behalf Of Santosh
CAPE> Sent: Thursday, March 19, 2009 9:37 PM
CAPE> To: r-h...@r-project.org
CAPE> Subject: [R] which.na
CAPE> Hi R- users
CAPE> I was wondering if there is any function equivalent to which.na used
in S+?
CAPE> Thanks much in advance!
CAPE> Regards,
CAPE> Santosh
CAPE> [[alternative HTML version deleted]]
CAPE> ______________________________________________
CAPE> r-h...@r-project.org mailing list
CAPE> https://stat.ethz.ch/mailman/listinfo/r-help
CAPE> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
CAPE> and provide commented, minimal, self-contained, reproducible code.
CAPE> ______________________________________________
CAPE> r-h...@r-project.org mailing list
CAPE> https://stat.ethz.ch/mailman/listinfo/r-help
CAPE> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
CAPE> and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
