[R] Re: trailing zeroes

[Prof Brian Ripley]

> Date: Fri, 26 Feb 1999 09:59:39 +0000
> From: Bendix Carstensen <bxc at svs.dk>

> When you require 2 digits you expect to find 5.96 printed

Correction, _you_ expect!  Very few computer programs do that.  You
cannot `require' two digits by options(digits=2):  ?options says

  digits: controls the number of digits to print when print-
          ing numeric values. It is a suggestion only.

> as 6.0, i.e. a number somewhere between 5.95 and 6.04999999999999.
> This is apparently not always the case for R.
> Why does 0 have a special status as trailing digit?
> 
> > options(digits=2)
> > x <- c(59.6,59.4)
> > x
> [1] 60 59
> > x/10
> [1] 6.0 5.9
> > x[1]/10
> [1] 6

Because that is how the ASCII C printing functions work.  Ultimately
print() calls sprintf with a %x.yf format. What happens depends on how
that is implemented on your system.

S-PLUS has an option nsmall to format to do precisely this, and there
was a question asking how to do it on s-news today.  I have thought for
a while that we need to implement something like this in R: maybe I had
better do it....

-- 
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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