[R] Bug in "is" ?

Martin Maechler maechler at stat.math.ethz.ch
Wed Sep 24 14:42:32 CEST 2008

>>>>> "KJ" == Keith Jewell <k.jewell at campden.co.uk>
>>>>>     on Wed, 24 Sep 2008 09:46:08 +0100 writes:

    KJ> "7" is an integer, but it's also a real.
    KJ> In R '?is'  and '?is.integer' are clear that you're testing the class(es) of 
    KJ> objects, not their values.
    KJ> I can't comment on the relationship with "S Programming"

I can:

In S, and S-plus upto version 3.4,
numeric constants such as '7' where  "double" as they are in R.

Then in S-plus 5.1, they became "integer",
and there were tools so users could change all(!!) their S
scripts to use '7.' instead of '7' in all places where numeric
constants were seen, in order to keep behavior back compatible.

R never made such a step (backwards ;-), and never will,
notably since in R we had introduced the explicit long (= long
integer) constants, using the 'L' suffix,
i.e.,  7L is "integer"
        7 is "double"

Note however that for both, is.numeric(.) is fulfilled and 
class(.) and mode(.) return "numeric".
Only typeof(.), storage.mode(.)  or  str(.) 
(or functions building on these) tell you the difference.

Martin Maechler, ETH Zurich and R core team

[And, yes, if you think further and are wondering: 
 If we'd design things from scratch, we would only have S4
 classes and "double" would be a proper class and 
 "numeric" would be the class union of {"integer", "double"}

    KJ> <ctu at bigred.unl.edu> wrote in message 
    KJ> news:20080924000503.1fsyrqf6zokk40kg at wm-imp-1.unl.edu...
    >> This is really bothering me! In the Dr. Venables and Dr. Ripley's book  "S 
    >> Programming" Page 105
    >> shows that
    >>> c(is(10,"integer"),is(10.5,"integer"))
    >> [1] T F
    >> But I try this in R 2.7.2 it shows
    >>> c(is(10,"integer"),is(10.5,"integer"))
    >> [1] FALSE FALSE
    >> Does anyone know what is going on here?
    >> Appreciate,
    >> Chunhao
    >> Quoting Yihui Xie <xieyihui at gmail.com>:
    >>> 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>
    >>> Phone: +86-(0)10-82509086 Fax: +86-(0)10-82509086
    >>> Mobile: +86-15810805877
    >>> Homepage: http://www.yihui.name
    >>> School of Statistics, Room 1037, Mingde Main Building,
    >>> 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

    KJ> ______________________________________________
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    KJ> https://stat.ethz.ch/mailman/listinfo/r-help
    KJ> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    KJ> and provide commented, minimal, self-contained, reproducible code.

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