R devel - Jan 2003 - (PR#2453) ctest package: wilcox.test() produces integer

We've seen the integer overflow problem in ks.test before, easily solved.

The help page says x and y must be numeric, so this is user error.  I've
added tests to the code.

Why do people file bug reports without reading the help/man page?

On Tue, 14 Jan 2003 bates@stat.wisc.edu wrote:
> This was filed as a bug report on the Debian r-base package.  It is
> more properly a bug report on the ctest package in R.  
> 
> The default method for wilcox.test manipulates x and y without
> checking the class or data.class of these objects.  Possible solutions
> are
>  - create wilcox.test.factor (if appropriate)
>  - check the class and/or data.class of x and y in wilcox.test.default
>    and produce error messages or warnings for inappropriate objects
>  - coerce to numeric unconditionally (probably not a good idea)
> 
> Martin Michlmayr <tbm@cyrius.com> writes:
> 
> > Package: r-base
> > Version: 1.5.0-2 / 1.6.1.cvs.20030103-1
> > Severity: normal
> > 
> > I have some ordinal data and I wanted to perform an u-test.  However,
> > a problem occured:
> > 
> > > x <- read.table("spss-3.txt", header=TRUE)
> > > a = factor(x$a)
> > > b = factor(x$b)
> > > summary(a)
> >     1     2     3     4     5     6 
> > 23900 20362 15238 10007  3399   472 
> > > summary(b)
> >     1     2     3     4     5     6 
> > 23809 20649 15069  9952  3415   484 
> > > wilcox.test(a, b)
> > 
> >         Wilcoxon rank sum test with continuity correction
> > 
> > data:  a and b 
> > W = 5384330884, p-value = NA
> > alternative hypothesis: true mu is not equal to 0 
> > 
> > Warning messages: 
> > 1: "-" not meaningful for factors in: Ops.factor(x, mu) 
> > 2: NAs produced by integer overflow in: n.x * n.y 
> > 3: NAs produced by integer overflow in: n.x * n.y 
> > > 
> > 
> > Now there appear to be two issues: First of all, the NAs produced by
> > integer overflow.  Since they go away when I use less data, this looks
> > like an R bug with big data sets.  When I use less data, the warning
> > goes away:
> > 
> > 57:tbm@arborlon: ~] wc -l s
> >   40000 s
> > 
> > > summary(a)
> >     1     2     3     4     5     6 
> > 13034 11086  8341  5412  1869   257 
> > > summary(b)
> >     1     2     3     4     5     6 
> > 13034 11086  8341  5412  1869   257 
> > > wilcox.test(a, b)
> > 
> >         Wilcoxon rank sum test with continuity correction
> > 
> > data:  a and b 
> > W = 1599920001, p-value = < 2.2e-16
> > alternative hypothesis: true mu is not equal to 0 
> > 
> > Warning message: 
> > "-" not meaningful for factors in: Ops.factor(x, mu) 
> > > 
> > 
> > 
> > However, I still don't know what the other warning is.  I dont
have an
> > "-" in my data.  I reduced the data to 2 lines and the
problem still
> > occurs:
> > 
> > > summary(a)
> > 2 3 
> > 1 1 
> > > summary(b)
> > 2 3 
> > 1 1 
> > > wilcox.test(a, b)
> > 
> >         Wilcoxon rank sum test
> > 
> > data:  a and b 
> > W = 4, p-value = 0.3333
> > alternative hypothesis: true mu is not equal to 0 
> > 
> > Warning message: 
> > "-" not meaningful for factors in: Ops.factor(x, mu) 
> > > 
> > 
> > The file is:
> > 
> > 67:tbm@arborlon: ~] cat s
> > a   b
> > 2   4
> > 3   1
> > 68:tbm@arborlon: ~] 
> > 
> > 
> > I'm not an R expert, so this might be a pilot error; but I
don't see
> > where.
> > 
> > 
> > -- System Information:
> > Debian Release: 3.0
> > Architecture: i386
> > Kernel: Linux regression 2.4.19-686 #1 Thu Aug 8 21:30:09 EST 2002
i686
> > Locale: LANG=en_US, LC_CTYPE=en_US
> > 
> > Versions of packages r-base depends on:
> > ii  r-base-core                   1.5.0-2    GNU R core of statistical
computin
> > ii  r-base-html                   1.5.0-2    GNU R html docs for
statistical co
> > ii  r-base-latex                  1.5.0-2    GNU R LaTeX docs for
statistical c
> > 
> > -- no debconf information
> > 
> > 
> > -- 
> > Martin Michlmayr
> > tbm@cyrius.com
> > 
> > 
> 
> 
-- 
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