[R] tests for NULL objects

[Benilton Carvalho]

Thank you Bert,

Sorry if it sounded like a complain, this is not what I meant.

The situation I had was: given a vector "v" containing integers or  
NA's, I wanted to know if after excluding the NA's all the remaining  
observations were 2's.

Naively, I assumed that:

all(na.omit(v) == 2)

would do the work, but now I see that it fails if, for example,

v = rep(NA, 10)

But that's okay, just a matter of adding an extra test (already done).

When I asked for clarification about the reasons for this, I assumed  
that:

if all(v) is TRUE ==> any(v) is TRUE; for all " (logical) v"...

When actually:

if all(v) is TRUE ==> any(v) is TRUE; for all "(logical) v of length  
 >= 1".

Thank you,

benilton

On Nov 29, 2006, at 6:35 PM, Bert Gunter wrote:

> Merely convention.
>
> NULL == 2  <==> logical(0), that is, a logical vector of length 0.  
> It makes
> sense (at least to me) that any(logical(0)) is FALSE, since no  
> elements of
> the vector are TRUE. all(logical(0)) is TRUE since no elements of  
> the vector
> are FALSE.
>
> I think these are reasonable and fairly standard conventions, but  
> even if
> you disagree, they are certainly not worth making a fuss over and  
> certainly
> cannot be changed without breaking a lot of code, I'm sure.
>
> Bert Gunter
> Nonclinical Statistics
> 7-7374
>
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Benilton  
> Carvalho
> Sent: Wednesday, November 29, 2006 2:21 PM
> To: R-Mailingliste
> Subject: [R] tests for NULL objects
>
> Hi Everyone,
>
> After searching the subject and not being successful, I was wondering
> if any you could explain me the idea behind the following fact:
>
> all(NULL == 2)  ## TRUE
> any(NULL == 2) ## FALSE
>
> Thanks a lot,
>
> Benilton
>
> --
> Benilton Carvalho
> PhD Candidate
> Department of Biostatistics
> Johns Hopkins University
>
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