[Rd] ctest package: wilcox.test() produces integer overflow (PR#2453)

[bates@stat.wisc.edu]

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
> 
> 

-- 
Douglas Bates                            bates@stat.wisc.edu
Statistics Department                    608/262-2598
University of Wisconsin - Madison        http://www.stat.wisc.edu/~bates/