[Rd] identical(0, -0)

Martin Maechler maechler at stat.math.ethz.ch
Sat Aug 22 00:00:44 CEST 2009

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'. 

I'm open for better names of arguments, but will not accept "_"
in the argument names {just my taste; no reason for argueing...}.

I've practically finished both C- and R- and Rd-code, but can
still adapt to proposals if there are good reasons for it.

Martin Maechler, ETH Zurich

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