integer functions {was [Rd] Inconsistencies (PR#550)}
maechler@stat.math.ethz.ch
maechler@stat.math.ethz.ch
Mon, 22 May 2000 12:22:12 +0200 (MET DST)
>>>>> "BDR" == Prof Brian D Ripley <ripley@stats.ox.ac.uk> writes:
BDR> On Mon, 22 May 2000 berwin@maths.uwa.edu.au wrote:
>> Dear all,
>>
>> I was playing around with some C-code that I dynamically linked to R
>> and noticed the following inconsistency:
> > dat <- matrix(1,3,3)
> > is.double(dat)
> [1] TRUE
> > is.integer(dat)
> [1] FALSE
> > dat <- matrix(1:9,3,3)
> > is.double(dat)
> [1] FALSE
> > is.integer(dat)
> [1] TRUE
>> How did I find out? I passed `dat' to a double * in the C-code and
>> printed out the matrix from C. But in the .C() call I just passed
>> down `dat' and forgot to coerce to double via `as.double(dat)'. Of
>> course the print out from the C routine was garbage, but since I used
>> dat <- matrix(1,3,3)
>> first, I was confused. Note that R says
>> that `dat' is.double! But it seems to pass dat to C as an integer
>> matrix nevertheless! Using the second matrix it became clear to me
>> why I saw garbage being printed out from the C-routine. My question
>> is now why does the first `is.double(dat)' returns `TRUE'?
BDR> Because it is double! This refers to the storage mode, not the
BDR> mathematical properties of the object's content.
exactly!
Please (everyone who needs, probably Berwin doesn't) *do*
study ?storage.mode and ?mode with some care
BDR> I can find no inconsistency. 1 is double, and 1:9 is integer
BDR> (just as in S-PLUS 3.x). Why should this not be the case?
BDR> Currently the only time in R you are likely to get an integer
BDR> result is a : or seq expression, but you are not supposed to rely
BDR> on this.
Well, "Values:" in ?seq says
>> Value:
>> The result is of `mode' `"integer"' if `from' is (numerically
>> equal to an) integer.
on which I do rely..
Also, there are other functions guaranteeing an integer (or NA / NULL)
result, at least
o length()
o dim()
o ncol(), nrow()
---
o min() and max() --- when all args are integers
o "+" and "-" if the args are integers
-- however that might change: Currently, there's no overflow detection!
BDR> (Since I know you have a copy, this is exactly the
BDR> problem of the wam example on page 203 of `S Prograaming'.)
BDR> For example, if printit.c is
<... instructive example...>
Martin Maechler <maechler@stat.math.ethz.ch> http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum LEO D10 Leonhardstr. 27
ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND
phone: x-41-1-632-3408 fax: ...-1228 <><
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