Hi
r-help-boun...@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.fo...@diamond.ac.uk
> Alt Email: j.fo...@imperial.ac.uk
>
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