[R] Built-in function for extracting mantissa and exponent of a numeric
Prof Brian Ripley
ripley at stats.ox.ac.uk
Sun Jun 23 13:05:41 CEST 2013
On 23/06/2013 10:54, Søren Højsgaard wrote:
> Dear all,
> Given a number
> is there a built-in function for extracting 1.234 and 12 ?
No, because that is not how the number is stored (and in fact the value
stored is a binary fraction with a slightly different value).
> The following "hack" seems clumpsy:
format() is doing a lot of work to produce a decimal approximation to
'x', including choosing the precision.
It is not clear what you want: if you merely want to express x as a*10^b
for 1 <= a < 10 then
b <- floor(log10(x))
a <- x/10^b
does the job (but might get values of a very slightly less than 1 or
above 10, so if you care this might need checking and refinement).
>> a<-strsplit(format(x, scientific=T),"e")[]
>  "1.234" "+12"
>  1.234
>  12
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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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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