[R] identical(length(x), 1) returns FALSE, but print(length(x)) is 1, length(x)==1 is TRUE, and is.integer(lenght(x)) is TRUE????

[Gavin Simpson]

On Tue, 2009-09-15 at 17:16 +0100, Corrado wrote:
> Dear R,
> 
> the condition: 
> 
> identical(length(x),1) returns FALSE 
> 
> but
> 
> print(length(x))
> 
> returns 1 and:
> 
> is.vector(x) is TRUE.
> is.integer(length(x)) is TRUE
> length(x) ==1 is TRUE
> 
> I am puzzled.

The key is noticing that 1 is a double:

[note you don't give us your x so I'm making this up - This is what
Duncan was going on about in an earlier thread, give us something we can
just paste into R and it works]

> x <- 2
> identical(length(x),1)
[1] FALSE
> class(1)
[1] "numeric"
> typeof(1)
[1] "double"
> typeof(length(x))
[1] "integer"

and therein lies the reason for the difference.

If you want to force 1 to be integer, the append and L, i.e.:

> identical(length(x),1L)
[1] TRUE

Are you really looking for all.equal()?

> isTRUE(all.equal(length(x), 1))
[1] TRUE

HTH

G
> 
> Regards
-- 
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
 ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
 Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
 Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
 UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%