

   FFaaccttoorr LLeevveellss

        levels(x) <- value

   DDeessccrriippttiioonn::

        `levels<-' provides a way to alter the levels attribute
        of factor.  `value' can be a vector of character
        strings with length equal to the number of levels of
        `x', or a named list specifying how to rename the lev-
        els.

   SSeeee AAllssoo::

        `factor', `levels', `levels<-', `nlevels'.

   EExxaammpplleess::

        # assign individual levels
        x <- gl(2, 4, 8)
        levels(x)[1] <- "low"
        levels(x)[2] <- "high"

        # or as a group
        y <- gl(2, 4, 8)
        levels(y) <- c("low", "high")

        # combine some levels
        z <- gl(3, 2, 12)
        levels(z) <- c("A", "B", "A")

        # same, using a named list
        z <- gl(3, 2, 12)
        levels(z) <- list(A=c(1,3), B=2)

