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\name{levels}
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\name{levels}
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\alias{levels}
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\alias{levels<-}
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\alias{levels<-.default}
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\alias{levels<-.factor}
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\title{Levels Attributes}
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\title{Levels Attributes}
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\usage{
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\usage{
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levels(x)
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levels(x)
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levels(x) <- value
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levels(x) <- value
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}
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}
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\alias{levels}
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\alias{levels<-}
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\alias{levels<-.default}
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\description{
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\description{
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  \code{levels} provides access to the levels attribute of a variable.
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  \code{levels} provides access to the levels attribute of a variable.
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  The first form returns the value of the levels of its argument
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  The first form returns the value of the levels of its argument
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  and the second sets the attribute.
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  and the second sets the attribute.
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  The most important method is that for \code{\link{factor}}s:
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  The most important method is that for \code{\link{factor}}s:
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}
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}
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\arguments{
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\arguments{
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  \item{x}{an object, for example a factor.}
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  \item{x}{an object, for example a factor.}
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  \item{value}{A valid value for \code{levels(x)}.
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  \item{value}{A valid value for \code{levels(x)}.
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    For the default method, \code{NULL} or a character vector.}
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    For the default method, \code{NULL} or a character vector.  For the
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    \code{factor} method, a vector of character strings with length at
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    least the number of levels of \code{x}, or a named list specifying how to
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    rename the levels.}
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}
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}
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\references{
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\references{
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
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  \emph{The New S Language}.
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  \emph{The New S Language}.
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  Wadsworth \& Brooks/Cole.
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  Wadsworth \& Brooks/Cole.
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}
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}
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\seealso{
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\seealso{\code{\link{levels<-.factor}}, \code{\link{nlevels}}.
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  \code{\link{nlevels}}.
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}
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\examples{
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## assign individual levels
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x <- gl(2, 4, 8)
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levels(x)[1] <- "low"
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levels(x)[2] <- "high"
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x
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## or as a group
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y <- gl(2, 4, 8)
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levels(y) <- c("low", "high")
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y
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## combine some levels
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z <- gl(3, 2, 12)
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levels(z) <- c("A", "B", "A")
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z
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## same, using a named list
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z <- gl(3, 2, 12)
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levels(z) <- list(A=c(1,3), B=2)
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z
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## we can add levels this way:
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f <- factor(c("a","b"))
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levels(f) <- c("c", "a", "b")
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f
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f <- factor(c("a","b"))
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levels(f) <- list(C="C", A="a", B="b")
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f
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}
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}
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\keyword{category}
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\keyword{category}