R devel - Sep 2008 - Bug in "is" ?

Hi R users
Is there anything wrong in "is" function? (R 2.7.2)
I believe that everyone will agree that "7" is an integer, right? but
why R shows 7 is not an integer
> is.integer(7)
[1] FALSE
> is(7,"integer")
[1] FALSE
> is(as.integer(7), "integer")
[1] TRUE

Thank you very much in advance
Chunhao

Yes, everyone will agree "7" is an integer, but I don't think
computers will agree too :-) R thinks it's a double-precision number,
except when you explicitly specify it as an integer (say,
as.integer()).
> class(7)
[1] "numeric"
> is.double(7)
[1] TRUE

Regards,
Yihui
--
Yihui Xie <xieyihui at gmail.com>
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Renmin University of China, Beijing, 100872, China



On Wed, Sep 24, 2008 at 12:40 PM,  <ctu at bigred.unl.edu>
wrote:
> Hi R users
> Is there anything wrong in "is" function? (R 2.7.2)
> I believe that everyone will agree that "7" is an integer, right?
but why R
> shows 7 is not an integer
>
>> is.integer(7)
>
> [1] FALSE
>>
>> is(7,"integer")
>
> [1] FALSE
>>
>> is(as.integer(7), "integer")
>
> [1] TRUE
>
> Thank you very much in advance
> Chunhao
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

quote:
No doubt, 7.0 is integer in math. But if people can write 7 why people 
need to write 7.0 (I do not see any reason to do this).
endquote

First off, in physics, engineering, chem, etc.  there is a well-known 
rule that 7 implies an error of +/- 0.5 while 7.0 implies an error of 
+/-0.05 .  (actually,  the preferred notation is x.yEz so that the 
physical size of the number doesn't cause a bunch of zeroes to imply 
false precision)

Next, aside from storage reasons (if you're writing machine code or 
comms packet code),  there are times when one wishes to stay in the 
integer world as opposed to the floating-point world.  There's tons of 
literature out there about binary representation of floats, 
binary-coded-decimal, and on and on.


Carl