On Fri, Aug 24, 2012 at 12:48:54PM +0200, Frederik Bertling wrote: > Hi, > > I'm doing some easy calculations to normalize some values. This looks like > this: > > x=mean(a+b+c+d ...) > a=a-x > b=b-x > c=c-x > d=d-x > ... > mean(a+b+c+d ...) ---> Should now be 0! > However, I'm getting results like -2.315223e-18 > This is really near to 0 but not very aesthetic. > > Can I prevent this? Or is this behaviour desired?
Hi. This is a consequence of the limited precision, which is used for speed. Examples of this type exist also for the decimal arithmetic. Using 3 digit precision, the arithmetic mean of the three numbers 1.02, 1.01, 1.01 is 1.01. So, the sum of the differences 1.02 - 1.01 1.01 - 1.01 1.01 - 1.01 is not zero. See functions zapsmall(), all.equal(). Hope this helps. Petr Savicky. ______________________________________________ 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.
