R help - Sep 2009 - identical(length(x), 1) returns FALSE, but print(length(x)) is 1, length(x)==1 is TRUE, and is.integer(lenght(x)) is TRUE????

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.

Regards
-- 
Corrado Topi

Global Climate Change & Biodiversity Indicators
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk

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.
> 
> Regards

 > is.integer(length(x))
[1] TRUE
 > is.integer(1)
[1] FALSE


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


Uwe Ligges

Hi,

On Sep 15, 2009, at 12:16 PM, 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.
But is.integer(1) is FALSE
and identical(length(x), 1L) is TRUE

... ouch ...

I guess the lesson learned is that:

identical() != =
-steve

--
Steve Lianoglou
Graduate Student: Computational Systems Biology
   |  Memorial Sloan-Kettering Cancer Center
   |  Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact

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
-- 
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 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
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On Tue, 2009-09-15 at 12:22 -0400, Steve Lianoglou
wrote:
> Hi,
<snip />
> I guess the lesson learned is that:
> 
> identical() != =
Indeed, and ?identical explains some of the motivation behind the
function identical and the examples of said help page include the
problem the OP faced... now where was that posting guide...

G

-- 
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
 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
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%

On Tue, 2009-09-15 at 17:28 +0100, Gavin Simpson wrote:
> On Tue, 2009-09-15 at 17:16 +0100, Corrado wrote:
> > Dear R,
<snip />
> 
> Are you really looking for all.equal()?
> 
> > isTRUE(all.equal(length(x), 1))
> [1] TRUE
Please ignore that bit of rubbish above, clearly that is not what is
required or wanted. Missed my afternoon coffee...

G
> 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
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%