[Rd] identical(0, -0)

[Henrik Bengtsson]

On Sat, Aug 22, 2009 at 1:22 AM, Petr Savicky<savicky at cs.cas.cz> wrote:
> On Sat, Aug 22, 2009 at 12:00:44AM +0200, Martin Maechler wrote:
>> I have taken up the issue now,
>> and after thinking, studying the source, trying to define a
>> 'method = <string>' argument, came to the conclusion that both
>> the implementation and documentation (and source code "self-explanation")
>> are easiest to program, maintain, and understand,
>> if I introduce explicit binary switches,
>> so I now  propose the following R-level interface which keeps
>> the current behavior the default:
>>
>> >> Usage:
>> >>
>> >>      identical(x, y, num.EQ = TRUE, one.NA = TRUE, attrib.asSet = TRUE)
>> >>
>> >> Arguments:
>> >>
>> >>     x, y: any R objects.
>> >>
>> >>   num.EQ: logical indicating if ('double' and 'complex' non-'NA')
>> >>           numbers should be compared using '==', or by bitwise
>> >>           comparison.  The latter (non-default) differentiates between
>> >>           '-0' and '+0'.
>> >>
>> >>   one.NA: logical indicating if there is conceptually just one numeric
>> >>           'NA' and one 'NaN';  'one.NA = FALSE' differentiates bit
>> >>           patterns.
>> >>
>> >> attrib.asSet: logical indicating if 'attributes' of 'x' and 'y' should
>> >>           be treated as _unordered_ tagged pairlists ("sets"); this
>> >>           currently also applies to 'slot's of S4 objects.  It may well
>> >>           be too strict to set 'attrib.asSet = FALSE'.

My only comment is to make the argument notation a bit more consistent:

  (num.Eq, one.NA, attrib.as.set)

or

  (numEq, oneNA, attribAsSet)

Also, maybe "single" instead of "one".

Thanks

Henrik

>
> I appreciate having several binary switches. Besides the arguments above,
> this is also useful for an interactive use of identical(), for example,
> for debugging purposes. If there is a difference between objects, then
> the switches allow to get more information concerning what is the type
> of the difference.
>
>> I'm open for better names of arguments, but will not accept "_"
>> in the argument names {just my taste; no reason for argueing...}.
>
> I would slightly prefere one.NaN instead of one.NA. In IEEE 754 terminology,
> R's 'NA's are a subset of 'NaN's. So. NaN is a bit more general notion,
> although in R, the sets of 'NA's an 'NaN's are disjoint. Moreover, the
> name one.NaN specifies more clearly, that the issue is important only
> for numeric types and not, for example, for integer.
>
> Petr.
>
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