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

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