[R] evil attributes

David Winsemius
Sun, 11 Apr 2021 21:06:42 -0000

On 4/11/21 11:46 AM, Viechtbauer, Wolfgang (SP) wrote:
> The is.vector() thing has also bitten me in the behind on a few occasions.
When I want to check if something is a vector, allow for it to possibly have
some additional attributes (besides names) that would make is.vector() evaluate
to FALSE, but evaluate to FALSE for lists (since is.vector(list(a=1, b=2)) is
TRUE -- which also wasn't what I had initially expected before reading the
documentation), I use:
>
> .is.vector <- function(x)
>     is.atomic(x) && !is.matrix(x) && !is.null(x)
>
> This might also work:
>
> .is.vector <- function(x)
>     is(x, "vector") && !is.list(x)

That will allow expression vectors to return TRUE, but they are not
atomic so they would be excluded by your current version.

--

David.

>
> I am sure there are all kinds of edge (and probably also not so edge) cases
where these also fail to work properly. Kinda curious if there are better
approaches out there.


You might want to exclude expression vectors as well.



> Best,
> Wolfgang
>
>> -----Original Message-----
>> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
Therneau, Terry
>> M., Ph.D. via R-help
>> Sent: Saturday, 10 April, 2021 16:12
>> To: R-help
>> Subject: Re: [R] evil attributes
>>
>> I wrote: "I confess to being puzzled WHY the R core has decided on
this
>> definition..."
>> After just a little more thought let me answer my own question.
>>
>> a. The as.vector() function is designed to strip off everything
extraneous and
>> leave just
>> the core.?? (I have a mental image of Jack Webb saying "Just the
facts
>> ma'am"). ? I myself
>> use it freqently in the test suite for survival, in cases where I'm
checking the
>> corrent
>> numeric result and don't care about any attached names.
>>
>>  ?b. is.vector(x) essentially answers the question "does x look
like a result of
>> as.vector?"
>>
>> Nevertheless I understand Roger's confusion.
>>
>> --
>> Terry M Therneau, PhD
>> Department of Quantitative Health Sciences
>> Mayo Clinic
>> therneau at mayo.edu
>>
>> "TERR-ree THUR-noh"
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