[R] evil attributes

Viechtbauer, Wolfgang (SP)
Sun, 11 Apr 2021 18:46:02 -0000

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)

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.

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"