On Tue, 27 Apr 2010, Greg Snow wrote:
I am working with the mcnemar.test function and the help does not show a
maintainer/author, but it is part of the stats package.
My issue is that I want to use the test on 2 variables with possible
values of 0:3, in one of the tests one of the variables does not
have any 3's, so to make sure that the matrix is square I do:
x <- factor(x, levels=0:3)
y <- factor(y, levels=0:3)
If I run mcnemar.test on the table of x and y then everything works fine, but
if I pass in x and y without running table first then I get an error about both
variables needing to have the same number of levels (which they did when I
passed them in). The problem occurs because the function when handed the raw
data does its own conversion to factor using the factor function which drops
the unused level in the one variable. A simple fix should be to replace the
call to factor with a call to as.factor (which will not change anything for
variables that are already factors and therefore not drop levels). I cannot
imagine any code that would break from this change, but that could just be a
lack of imagination on my part.
So, can anyone think of a reason not to change factor to as.factor?
Given the description
If \code{x} is a matrix, it is taken as a two-dimensional contingency
table, and hence its entries should be nonnegative integers.
Otherwise, both \code{x} and \code{y} must be vectors of the same
length. Incomplete cases are removed, the vectors are coerced into
factor objects, and the contingency table is computed from these.
it should 'coerce'.
Is this worth a bug report/enhancement request?
Not necessary, I'll change this in R-patched. Thanks for pointing it
out.
sessionInfo()
R version 2.11.0 (2010-04-22)
i386-pc-mingw32
locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] tools_2.11.0
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.s...@imail.org
801.408.8111
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--
Brian D. Ripley, rip...@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, UKFax: +44 1865 272595
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