Hello,
Just as a complement, if you want to see a solution, and why.
x <- 3/5
y <- 2/5
z <- 1/5
#
x - (y + z) # not zero
x == y + z
all.equal(x, y + z)
#
x - y - z # not zero
x - y == z
all.equal(x - y, z)
# To see why it works: abs diff less than tolerance
equal <- function(x, y, tol=.Machine$double.eps) abs(x - y) < tol
equal(x, y + z)
equal(x - y, z)
Hope this helps,
Rui Barradas
Em 24-06-2012 23:14, Andreia Leite escreveu:
Thanks a lot for your explanation!
I see the point and I think I'll solve my question using a different method!
Andreia Leite
On Sun, Jun 24, 2012 at 10:53 PM, Oliver Ruebenacker <cur...@gmail.com>wrote:
Hello,
The FAQ answer 7.31 may be confusing to noobs and the referenced
paper is long. The essence is:
(1) It's not an R issue, it is a floating point (flop) arithmetic issue.
(2) The issue is that flop arithmetic is almost always only approximate.
(3) Therefore, asking for exact equality of two flops is almost
always a mistake.
(4) In simple cases, you can take the difference of two flops and
ask whether it is good enough
(5) For extended calculations, you need to keep in mind that errors
propagate and accumulate.
(6) Some ill-defined problems may lead to "solutions" that aren't
solutions (e.g. trying to invert a singular matrix)
(7) Some well-defined problems may defy a straight-forward approach
(e.g. solving stiff differential equations)
Take care
Oliver
On Sun, Jun 24, 2012 at 5:29 PM, Sarah Goslee <sarah.gos...@gmail.com>
wrote:
Please read R FAQ 7.31, Why doesn't R think these numbers are equal?
Sarah
On Sun, Jun 24, 2012 at 1:58 PM, Andreia Leite
<andreiaheitorle...@gmail.com> wrote:
Dear list,
I'm trying to do a loop where I should choose a cell of a data frame
comparing it with another. The code actually works for the majority of
the
loop but for some reason it doesn't and I can't figure out why.
When I tried to understand why I've noticed this:
dif[11]
[1] 118.8333
linhasUpdate[10,6]
[1] 118.8333
dif[11]==linhasUpdate[10,6]
[1] FALSE
Even though the values are the same R says they aren't! This happens for
some of the values (44) and for the others (128) it works fine.
Does anybody why is this happening or a way to fix it? I' using 2.15.0.
Thanks a lot!
Andreia Leite
--
--
Sarah Goslee
http://www.functionaldiversity.org
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Oliver Ruebenacker, Bioinformatics and Network Analysis Consultant
President and Founder of Knowomics
(http://www.knowomics.com/wiki/Oliver_Ruebenacker)
Consultant at Predictive Medicine
(http://predmed.com/people/oliverruebenacker.html)
SBPAX: Turning Bio Knowledge into Math Models (http://www.sbpax.org)
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
