Hello,
A classic of floating-point accuracy is
> 3/5 - 3/5
[1] 0
> 3/5 - (2/5 + 1/5)
[1] -1.110223e-16
> 3/5 - 2/5 - 1/5
[1] -5.551115e-17
Rui Barradas
Em 15-06-2012 18:18, David Winsemius escreveu:
On Jun 15, 2012, at 12:49 PM, Julia wrote:
Hello,
I wanted to compute the time differenze between to times:
first =as.POSIXct( "2012-06-15 16:32:39.0025 CEST")
second = as.POSIXct("2012-06-15 16:32:39.0086 CEST")
second - first
The result is
Time difference of 0.006099939 secs
instead of just 0.0061 secs
So R adds aditional numbers after the result.
It's a floating point representation issue. You don't really want to
change that value, but are asking to see something different:
> round ( second - first, 4)
Time difference of 0.0061 secs
I know I could round it in this case.
But I am working with a large data set and need to always get the
correct result.
difftime() does not work correct either.
Has anybody a suggestion how to get the correct result?
Use a computer system that runs on exact arithmetic?
Read FAQ 7.31
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
(And expect to read about 4-6 similar messages in the next hour.)
Thank you
Julia
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David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
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.
