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