From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Thu 18 Jan 2007 - 17:23:27 GMT

>>> Hello everyone,

*>>>
*

*>>> I use latex() (Hmisc) for report generation and thus have been affected by
*

*>>> the problem with rounding decimals described, for example, in this post:
*

*>>>
*

*>>> http://thread.gmane.org/gmane.comp.lang.r.general/73287/focus=73287
*

*>>>
*

*>>> In short, numbers often are printed with 15 or so decimals even if there
*

*>>> far less significant digits. The problem has been confirmed by Frank
*

*>>> Harrell and Thomas Dupont according to this post:
*

*>>>
*

*>>> http://thread.gmane.org/gmane.comp.lang.r.general/73172/focus=73186
*

*>>>
*

*>>> But it has still not been fixed. Rather than changing all my reports I
*

*>>> decided I'd look at format.df() in Hmisc myself and try to fix the problem
*

*>>> there. I found that the problem is not in Hmisc at all, but in R itself:
*

*>>>
*

>>> [1] 1.001

>>> [1] 1.001000000000000

>>> [1] 1.001000000000000

*>>>
*

*>>> This does not seem to be the behaviour described in the documentation,
*

*>>> which says:
*

*>>>
*

*>>> "The same number of decimal places is used throughout a vector,[sic!] This
*

*>>> means that digits specifies the minimum number of significant digits to be
*

*>>> used, and that at least one entry will be encoded with that minimum
*

*>>> number. However, if all the encoded elements then have trailing zeroes,
*

*>>> the number of decimal places is reduced until at least one element has a
*

*>>> non-zero final digit."
*

*>>>
*

*>>> If print.default() exhibited the behaviour desribed in the docs,
*

*>>> format.df() and thus latex() would work as advertised, I think. I would
*

*>>> have written a bug report instead of posting here, but the fact (?) that
*

*>>> Frank and Thomas have confirmed the bug seems to indicate that the problem
*

*>>> does indeed lie with Hmisc. Am I misunderstanding something here?
*

*>>>
*

*>>> I use R version 2.4.1 Patched (2007-01-13 r40470) on Windows.
*

>>> .Machine$double.eps

Date: Thu 18 Jan 2007 - 17:23:27 GMT

On Thu, 18 Jan 2007, Charles Dupont wrote:

> Prof Brian Ripley wrote: >> On Mon, 15 Jan 2007, Ulrich Keller wrote: >>

>>> Hello everyone,

>>>> print(1.001)

>>> [1] 1.001

>>>> options(digits=16) #format.df does this >>>> print(1.001)

>>> [1] 1.001000000000000

>>>> print(round(1.001, 3)) #rounding does not help

>>> [1] 1.001000000000000

>> >> The bug is that Hmisc uses more digits than the representation provides: >>

>>> .Machine$double.eps

>> [1] 2.22044604925031e-16 >> >> If it used 15 digits (as R does for as.character) all would be well. Since >> R has to do the calculations you quote in binary arithmetic, they are also >> subject to representation error and there is no way they can be done to 16 >> significant figures. (I've traced the example, and that is what happens.) >> See ?as.character for more details. >> > > Is there an R object that contains the value of DBL_DIG for the current > machine? I have checked '.Machine' and '.Platform' and neither have the > value of DBL_DIG in them.

No, but please do as I suggested and read ?as.character: it is 15 on all current platforms.

-- Brian D. Ripley, ripley@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 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Fri Jan 19 04:45:35 2007

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.1.8, at Thu 18 Jan 2007 - 20:30:29 GMT.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*