[Rd] [R] which.na

[William Dunlap]

If you are considering emulating the S/S+ which.na, which.nan,
etc., family of functions to save space you might also consider
the related anyMissing function (I don't know why it
isn't any.is.na to match the pattern).  anyMissing(x) returns
the same result as any(is.na(x)) or length(which.na(x)) but
stops scanning the input when it sees the first NA, saving time
and space in the common idiom of stopifnot(!any(is.na(x))).
(BTW, Should R have a stopif() function to avoid that double negative?)

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of Martin Maechler
> Sent: Friday, March 20, 2009 2:46 AM
> To: Charles.Annis at statisticalengineering.com
> Cc: 'Santosh'; R-devel at stat.math.ethz.ch
> Subject: Re: [Rd] [R] which.na
> 
> >>>>> "CAPE" == Charles Annis, P E 
> <Charles.Annis at 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 ) )
> 
> Martin Maechler, ETH Zurich (and R Core team)
> 
> 
>     CAPE> Charles Annis, P.E.
> 
>     CAPE> Charles.Annis at StatisticalEngineering.com
>     CAPE> phone: 561-352-9699
>     CAPE> eFax:  614-455-3265
>     CAPE> http://www.StatisticalEngineering.com
>  
> 
>     CAPE> -----Original Message-----
>     CAPE> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On
>     CAPE> Behalf Of Santosh
>     CAPE> Sent: Thursday, March 19, 2009 9:37 PM
>     CAPE> To: r-help at 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]]
> 
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> 
>     CAPE> ______________________________________________
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>     CAPE> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
>     CAPE> and provide commented, minimal, self-contained, 
> reproducible code.
> 
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