[R] Logical Indexing of vectors -- Odd Behavior or....
Uwe Ligges
ligges at statistik.uni-dortmund.de
Thu Mar 27 22:39:06 CET 2003
Joel Kincaid wrote:
>
> R-Community,
>
> I'm puzzled by the following behavior in R 1.6.2 and have found no
> reference to this in the archives:
>
> >P <- seq(.1,.9,by=.1)
>
> >P[P > .4]
> [1] 0.5 0.6 0.7 0.8 0.9
> as expected. However,
> >P[P > .3]
> [1] 0.3 0.4 0.5 0.6 0.7 0.8 0.9
> ???
> Which is unexpected. Furthermore on the logical side
> > P>.1
> [1] FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
> > P>.2
> [1] FALSE FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
> > P>.3
> [1] FALSE FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
> > P>.4
> [1] FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE TRUE
> > P>.5
> [1] FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE TRUE
> > P>.6
> [1] FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE
> > P>.7
> [1] FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE TRUE
>
> What's with .3 and .7? Any pointers to where I might find out the info
> would be greatly appreciated,
>
> I'm running 1.6.2 on windows XP,
> Sincerely,
>
> Joel F. Kincaid, Ph. D.
> Assistant Professor
> Department of Economics and Finance
> Franklin P. Perdue School of Business
> Salisbury University
> Salisbury Maryland, 21801
> Phone: (410) 548-4416
> Email: jfkincaid at salisbury.edu
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
a) It has nothing to do with indexing.
b) It not completely unexpected.
In seq() some computations are involved, hence it's just a very small
inaccuracy which is expected when working with limited machines such as
computers:
options(digits=22) # some more details ...
seq(.1, .9, .1) # Ah, that's it! ;-)
Uwe Ligges
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