[R] Odp: strange issue with "which" on "seq"

From: Petr PIKAL <petr.pikal_at_precheza.cz>
Date: Wed, 09 Jun 2010 13:54:32 +0200

Hi

r-help-bounces_at_r-project.org napsal dne 09.06.2010 13:16:40:

> Dear R community,
> I am puzzled by the following lines:
>
> > v <- seq(-0.5,0.5,by=0.1)
> > v
> [1] -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
> > which(v == -0.4)
> [1] 2
> > which(v == 0)
> [1] 6
> > which(v == 0.1)
> integer(0)
> > which(v == 0.2)
> integer(0)
> > which(v == 0.3)
> integer(0)
> > which(v == 0.4)
> [1] 10
> > which(v == 0.5)
> [1] 11
>
> Why "which" can only match some of the values in "v"? Are the numbers
> generated by "seq" not exact fractional numbers?
> Please, help me to understand this.

Well FAQ 7.31 was not here some time. Computing in binary results in finite precision of fractional numbers.

v <- seq(-0.5,0.5,by=0.1)
v[7]-0.1
[1] 8.326673e-17

Regards
Petr

>
> J
>
> Dr James Foadi PhD
> Membrane Protein Laboratory (MPL)
> Diamond Light Source Ltd
> Diamond House
> Harewell Science and Innovation Campus
> Chilton, Didcot
> Oxfordshire OX11 0DE
>
> Email : james.foadi_at_diamond.ac.uk
> Alt Email: j.foadi_at_imperial.ac.uk
>
> --
> This e-mail and any attachments may contain confidential...{{dropped:8}}
>
> ______________________________________________
> R-help_at_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.



R-help_at_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. Received on Wed 09 Jun 2010 - 11:57:14 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Wed 09 Jun 2010 - 12:30:29 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive