[R] log10(), floor() combo issue?

[Prof Brian Ripley]

You will find that a `fuzz', typically 1.0e-7, is added to quantities
before floor() or as.integer() all over R.  seq.default() is one example.

For log10(1000) we use log(1000)/log(10), and that is not a ratio of
integers.

On Mon, 14 Oct 2002, E.L. Willighagen wrote:

>
> Hi all,
>
> in my search for a nice binary2decimal method, I received this nice
> code (thanx to Uwe Ligges):
>
>  bindec <- function(b)
>    sum(as.integer(unlist(strsplit(b, ""))) * 2^(floor(log10(b)):0))
>
> It fails, however, with:
>
> > bindec(1000)
> [1] 4
> Warning message:
> longer object length
>         is not a multiple of shorter object length in:
> as.integer(unlist(strsplit(b, ""))) * 2^(floor(log10(b)):0)
>
> The reason is the combination of floor() and log10():
>
> log10(1000) = 3
>
> ok, but:
>
> floor(log10(1000)) = 2
>
> ? Ok, I can live with some floating point inaccuracy, but this seems
> at least a bit strange, and to me troublesome as it makes the bindec()
> method fail...
>
> I've also tried to force the output of log10(1000) into integer format
> with
>
> floor(as.integer(log10(b)))
>
> However, with the same disappointing results...
>
> Ideas?
>
> kind regards,
>
> Egon
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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