[R] Problems with the sort function!?

[Peter Dalgaard]

Kay Pilz <Kay.Pilz at ruhr-uni-bochum.de> writes:

> Hello All.
> 
> I am running R 2.0.0 with a Win XP operating system. The same problem occured
> with R 1.9.1 but not with R.1.3.1 on a Win NT computer.
> 
> My request is about the following problem with the sort function:
...
> Taking the difference of the first two entries yields
> 
> > s[1]-s[2]
> [1] -2.220446e-16
> 
> which seems to be a numerical artefact.
> 
> Is this a bug, or just a handling error by me?

You, I think. Consider for instance


> x <- c(1.313,1.314,1.315,1.316)
> diff(x) - 1e-3
[1]  1.118897e-16 -1.101549e-16  1.118897e-16
> sort(diff(x) - 1e-3)
[1] -1.101549e-16  1.118897e-16  1.118897e-16
> diff(sort(diff(x) - 1e-3)[1:2])
[1] 2.220446e-16


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907