[Rd] Documentation/software inconsistency in `:` and seq

[Martin Maechler]

Hi Stavros,

>>>>> "SM" == Stavros Macrakis <macrakis at alum.mit.edu>
>>>>>     on Tue, 23 Jun 2009 15:53:30 -0400 writes:

    SM> In 2.8.1/Windows:
    SM> According to ? :

    SM> Details:
    SM> For numeric arguments 'from:to' is equivalent to 'seq(from, to)' ...

that *is* definitely true as    seq(from,to)  leads to  return(from:to)

    SM> Value:
    SM> For numeric arguments, a numeric vector.  This will be of type
    SM> 'integer' if 'from' and 'to' are both integers and representable
    SM> in the integer type, otherwise of type 'numeric'....

    SM> The first claim is inconsistent with the second; it appears that the first
    SM> one is true and the second is false.

{1st, 2nd ... where do you start counting ?}

    SM> Actual behavior:

    SM> storage.mode(1:2.5) => integer
    SM> storage.mode(`:`(from=1L,to=2.5)) => integer   # just to be completely
    SM> explicit

    SM> But of course 2.5 is not an integer or equal to one.

Interestingly, because of an earlier posting on the topic,
two days ago (*), I have fixed the help page (and very slightly also
the code) of ":"  

[for R-devel (to be 2.10.0 in October) only, because R 2.9.1
 has already been in pre-release feature deep freeze ].


    SM> This is the same behavior as seq:

    SM> storage.mode(seq(1,2.5)) => integer
    SM> storage.mode(seq(from=1L,to=2.5)) => integer

{of course, as I mentioned above}

    SM> ---------------------------------

    SM> On the other hand, according to ? seq

    SM> Currently, the default method returns a result of type '"integer"'
    SM> if 'from' is (numerically equal to an) integer

    SM> This is not correct:

Yes, seq(from, to)  {without further arguments} and "default"
'from', indeed returns from:to
and hence should probably either defer to the ":" help page
or copy-paste from it.


Martin Maechler, ETH Zurich

--------------------------------------------
(*)
------------------------------------------------------------------------
r48823 | maechler | 2009-06-22 17:57:05 +0200 (Mon, 22 Jun 2009)
Improve doc of ":" {and code very slightly, at the boundary of MAX_INT}
------------------------------------------------------------------------



    >> seq(1e16,1e16+10)
    SM> [1] 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16 1e+16
    >> seq(1e16,1e16+10)-1e16
    SM> [1]  0  0  2  4  4  4  6  8  8  8 10   # not enough precision to represent
    SM> all the distinct integers, OK
    >> storage.mode(seq(1e16,1e16+10))
    SM> [1] "double"

    SM> In this case, the ? : documentation is correct:

    SM> This will be of type 'integer' if ... representable in the integer
    SM> type, otherwise of type 'numeric'.

    SM> [[alternative HTML version deleted]]
    	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  {I'm amazed that you still did not find out how to avoid the
   above, e.g., by following the posting guide ...}

    SM> ______________________________________________
    SM> R-devel at r-project.org mailing list
    SM> https://stat.ethz.ch/mailman/listinfo/r-devel