Petr,
Many thanks for this detailed explanation. It seems that the printing is
going to vary because it is not done by R. I will try alternative
numbers of significant digits: I had set options(digits=4) in an attempt
to avoid inter-platform printing differences, without really
understanding what was causing them.
Ruth
-------- Original Message --------
Subject: Re: [R] round giving different results on Windows and Mac
Date: Sat, 10 Mar 2012 10:08:21 +0100
From: Petr Savicky <savi...@cs.cas.cz>
To: r-help@r-project.org
On Fri, Mar 09, 2012 at 09:34:14PM +0000, Ruth Ripley wrote:
Dear all,
I have been running some tests of my package RSiena on different
platforms and trying to reconcile the results.
With Mac, the commands
options(digits=4)
round(1.81652, digits=4)
print 1.817
With Windows, the same commands print 1.816
I am not bothered which answer I get, but it would be nice if they were
the same. A linux box agreed with the Mac.
Hi.
I obtain the same difference between Linux (1.817) and
32 bit Windows (1.816). As Duncan said, the number 1.8165
is not exactly representable and printing it to 4
significant digits may depend on the platform, since
it is a middle case.
Note that options(digits=4) means rounding to 4 significant
digits, while round(1.81652, digits=4) is rounding to 4
digits in the fractional part. Try signif(1.81652, digits=4)
to get the same type of rounding as in options(digits=4).
The problem is not in round(), since
x <- round(1.81652, digits=4)
print(x, digits=20)
print(x, digits=4)
yields on Linux
[1] 1.8165000000000000036
[1] 1.817
and on 32 bit Windows
[1] 1.8165000000000000036
[1] 1.816
The difference is not due to R, since R is responsible
only for the choice of the number of printed digits
and not for the digits themselves. The digits are computed
by sprintf() on the given platform. So, the difference
seems to be there.
The command
sprintf("%5.3f", 18165/10000)
yields on Linux
[1] "1.817"
and on 32 bit Windows
[1] "1.816"
Thank you for the example.
Petr Savicky.
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--
Ruth M. Ripley, Email:r...@stats.ox.ac.uk
Dept. of Statistics, http://www.stats.ox.ac.uk/~ruth/
University of Oxford, Tel: 01865 282857
1 South Parks Road, Oxford OX1 3TG, UK Fax: 01865 272595
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and provide commented, minimal, self-contained, reproducible code.
