[Rd] is.vector(as.vector(x)) is FALSE

[Achim Zeileis]

On Sun, 17 Oct 2004 01:51:47 +0000 (UTC) Gabor Grothendieck wrote:

> 
> The following, which was recently discussions on the rcom-l list,
> is a situation where coercing x1mat to a vector using as.vector
> results in an object that is.vector says is not a vector:
> 
>      R> x1mat<-matrix(list(1,1.1,1+1i,"a",NA,NaN), 3, 2)
>      R> is.vector(as.vector(x1mat))
>      [1] FALSE

If you give it a particular mode, it produces a vector:

R> as.vector(x1mat, mode = "character")
[1] "1"    "1.1"  "1+1i" "a"    "NA"   "NaN" 
R> as.vector(x1mat, mode = "numeric")
[1] 1.0 1.1 1.0  NA  NA NaN
Warning messages: 
1: imaginary parts discarded in coercion 
2: out-of-range values treated as 0 in coercion to raw 

A somewhat similar and simpler example is:

R> x <- data.frame(a = 1:5, b = 6:10)
R> is.vector(as.vector(x))
[1] FALSE

because data.frames are also already vectors of mode "list". The man
page of as.vector provides a similar example with:

R> as.vector(x, mode = "numeric")
Error in as.vector(x, mode = "numeric") : (list) object cannot be
coerced to double

I had discussed this with Kurt (and maybe R-devel, but I cannot find it
in the archives) some time ago and the bottom line--if I recall
correctly--was that is.vector() and as.vector() do not behave in the
way that is.vector(as.vector(x)) always gives TRUE (or an error).

Z