On Sep 8, 2011, at 3:54 PM, Marc Schwartz wrote:
On Sep 8, 2011, at 2:42 PM, David Winsemius wrote:
On Sep 8, 2011, at 3:35 PM, Alexander Engelhardt wrote:
Am 08.09.2011 20:48, schrieb Marc Schwartz:
There was a post from Martin Maechler some years ago and I had to
search a bit to find it. For these sorts of issues, I typically
trust his judgement.
The post is here:
https://stat.ethz.ch/pipermail/r-help/2003-April/032471.html
His solution also handles complex numbers.
For those too lazy to follow
He is basically creating the function is.whole:
is.whole <- function(x)
is.numeric(x) && floor(x)==x
Are you sure? I thought the test would have been all.equal(x,
round(x,0) )
My reasoning was that 1.999999999999 should be considered 2 but
floor would make it 1.
David, I am confuzzled. Why would that be equal to 2?
So that sqrt(3) * sqrt(3) would be a "whole number". (It is true the
the floor based wholeness criterion would make sqrt(2)*sqrt(2)
Somehow it doesn't see "right" that only half of square roots of
integers that have been squared should pass the wholeness test:
> 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))})
+ }
> is.whole( sqrt(2)^2 )
[1] TRUE
> is.whole( sqrt(3)^2 )
[1] FALSE
x == 2
[1] FALSE
2 - x
[1] 1.000089e-12
# The default tolerance is .Machine$double.eps ^ 0.5
all.equal(x, 2, tol = .Machine$double.eps)
[1] "Mean relative difference: 5.000445e-13"
all.equal(x, 2, tol = .Machine$double.eps ^ 0.5)
[1] TRUE
x=1.999999999999
x
[1] 2
print(x, 15)
[1] 1.999999999999
floor(x)
[1] 1
isTRUE(all.equal(x, floor(x)))
[1] FALSE
all.equal(x, round(x,0))
[1] TRUE
Seems like the most appropriate way now. I'll make it so!
Very apropos on the 45th anniversary of Star Trek. :-)
Thanks for your help :-)
-- Alex
Cheers,
Marc
David Winsemius, MD
West Hartford, CT
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