"PhGr" == Philippe Grosjean <phgrosjean@sciviews.org>
on Wed, 8 Jan 2003 11:24:40 +0100 (MET) writes:
PhGr> as.integer() truncates doubles toward zero, as Splus
PhGr> does (at least v. 6.1 under Windows does). Thus:
(fortunately this is not OS dependent!)
>> look <- (10 * seq(14)) - 76
>> 10 * (73.1 + look)
PhGr>[1] 71 171 271 371 491 586 681 791 886 981 1101 1201 1301 1401
>> as.integer(10 * (73.1 + look))
PhGr>[1] 70 170 270 370 490 586 681 791 886 981 1101 1201 1301 1401
PhGr> ... It is not documented in R! I propose appending the following to
PhGr> as.integer.Rd:
I agree the doc should mention it.
I disagree with the warning section.
In R, our code really just uses something like
int asInt(double x) { return x; }
which makes use of C's "implicit casting".
I know looked in Kernighan & Ritchie (2nd Ed.; {3rd Ed would be better})
and found (p.197)
>> "A6.3 Integer and Floating"
>>
>> When a value of floating type is converted to integral type,
>> the fractional part is discarded. ...................
Hence this is (fortunately!) part of the C standard.
But I really think any decent programming language would do it
like that (many would not allow implicit coercion though..).
That's the reason I think the warning is not necessary; I'd
rather mention it by the way.
PhGr> \section{ WARNING }{ During coercion of doubles, real
PhGr> numbers are not rounded but truncated (the closest
PhGr> integer towards zero is returned). Attributes are
PhGr> deleted.}
PhGr> And I suggest adding the previous exemple in the
PhGr> corresponding section in as.integer.Rd. Moreover, the
PhGr> subset operation [] uses as.integer() and
PhGr> consequently, can suffer from the same syndrome. A
PhGr> WARNING section in Extract.Rd would be welcome too.
"suffer" and "syndrome" are not appropriate here IMHO.
Martin Maechler <maechler@stat.math.ethz.ch> http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum LEO C16 Leonhardstr. 27
ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND
phone: x-41-1-632-3408 fax: ...-1228 <><