[R] Testing for whole numbers
Martin Maechler
maechler at stat.math.ethz.ch
Thu Apr 17 18:05:55 CEST 2003
>>>>> "Tamas" == Tamas Papp <tpapp at axelero.hu>
>>>>> on Thu, 17 Apr 2003 16:47:30 +0200 writes:
Tamas> Is there a way in R to test if a given number is an integer, ie a
Tamas> whole number? I am not referring to the data type of a number, but to
Tamas> its value.
Tamas> That is to say, is.whole(pi-pi+2) would be TRUE, whereas is.whole(4/3)
Tamas> would be false. At the moment I am using
Tamas> is.whole <- function(a) { floor(a)==a }
Tamas> which is OK for real numbers, but not for complex ones (a+bi would be
Tamas> a whole number if both a and b are whole). Although it's obvious to
Tamas> test for the type of the argument and treat it accordingly, I am sure
Tamas> that there is a function for that in R.
Tamas> My questions are:
Tamas> 1. Is there a predefined function for this? I am not trying to
Tamas> reinvent the wheel, but I have searched help and found nothing
Tamas> relevant.
No, not in the standard packages at least.
Following your original, I'd recommend to use
is.whole <- function(a) {
(is.numeric(a) && floor(a)==a) ||
(is.complex(a) && floor(Re(a)) == Re(a) && floor(Im(a)) == Im(a))
}
or rather something like
is.whole <- function(a, tol = 1e-7) {
is.eq <- function(x,y) {
r <- all.equal(x,y, tol=tol)
is.logical(r) && r
}
(is.numeric(a) && is.eq(a, floor(a))) ||
(is.complex(a) && {ri <- c(Re(a),Im(a)); is.eq(ri, floor(ri))})
}
Tamas> 2. Would it make sense to propose the extension of
Tamas> floor, trunc etc to complex numbers? It would
Tamas> certainly make my life easier in many situations.
It would make sense to propose, yes.
[ Actually maybe another nice test bed for using S4 methods? ]
Even better, if you'd provide the necessary code patches.
But, then, you'd find that R (as well as the other S
implementations) are lacking much of complex number computing
facilities you might want to dream of.
To provide some of these would require a *lot* of more source
code, though that's not true for floor.
One reason for the lack of extensive complex support has been
the rare use of it in (main stream) statistics.
But, as said above: Improvements are welcome!
Martin Maechler <maechler at 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 <><
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