On Wed, 31 Mar 2004, Duncan Murdoch wrote:
> On Wed, 31 Mar 2004 12:24:38 -0500, Stephane DRAY
> <[EMAIL PROTECTED]> wrote :
>
> >Hello list,
> >I have used scan function to import data into R. I have done some analysis
> >and find strange results. I have found my problem : when importing data
> >with scan, this can slightly modify the data :
> >
> > > write(c(0.251,3.399,-0.481,0.266),"essai.txt")
> > > scan("essai.txt")
> >Read 4 items
> >[1] 0.251 3.399 -0.481 0.266
> > > print(scan("essai.txt"),17)
> >Read 4 items
> >[1] 0.25100000000000000 3.39900000000000000
> >-0.48099999999999998 0.26600000000000001
> >
> >
> >
> >Is it normal ? Is it a bug ?
>
> I think it's normal. Floating point formats aren't exact except for
> fractions with only powers of 2 in the denominator. There is no way
> to represent any of your values in the formats that R uses without
> slight errors.
>
> I do notice one oddity in the print routines in R:
>
> > x<-scan()
> 1: 0.266
> 2: 0.251
> 3:
> Read 2 items
> > print(x,17)
> [1] 0.26600000000000001 0.25100000000000000
> > x<-scan()
> 1: 0.266
> 2:
> Read 1 items
> > print(x,17)
> [1] 0.266
>
> I don't know why the second print() prints 0.266 differently from the
> first one. (This is in the 1.9.0 beta in Windows).
Because the precision applies to the smallest of the numbers.
--
Brian D. Ripley, [EMAIL PROTECTED]
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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