1\name{dropUnusedLevels}
2\alias{dropUnusedLevels}
3\title{Create Temporary Factor Subsetting Function}
4\description{
5Calling this function makes Hmisc have its pre-version 3.0 behavior in
6which the \R \code{[.factor} function was overridden by a customized
7version that caused unused \code{factor} \code{level}s to be dropped
8when the factor variable was subscripted (subsetted).
9\code{dropUnusedLevels()} creates a temporary version of \code{[.factor}
10in the global environment, which will take precedence.  To later make
11this function keep unused levels on subsetting, issue
12\code{options(drop.unused.levels=FALSE)} or just remove this temporary
13function from the environment by issuing
14\code{remove('[.factor',pos='.GlobalEnv')}.
15}
16\usage{
17dropUnusedLevels()
18}
19\author{Frank Harrell and Jens Oehlschlaegel}
20\seealso{\code{\link{factor}},\code{\link{[.factor}}}
21\examples{
22\dontrun{
23x <- factor(c('a','b','c'))
24x[1:2]  # keeps level c
25dropUnusedLevels()
26x[1:2]  # no c any more
27}}
28\keyword{category}
29\keyword{utilities}
30\keyword{programming}
31\keyword{methods}
32
33