levels                 package:base                 R Documentation

Levels Attributes

Description:

     'levels' provides access to the levels attribute of a variable.
     The first form returns the value of the levels of its argument and
     the second sets the attribute.

     The replacement form ('"levels<-"') of 'levels' is a generic
     function and new methods can be written for it. The most important
     method is that for 'factor's:

Usage:

     levels(x)
     levels(x) <- value

Arguments:

       x: an object, for example a factor.

   value: A valid value for 'levels(x)'. For the default method, 'NULL'
          or a character vector.  For the 'factor' method, a vector of
          character strings with length at least the number of levels
          of 'x', or a named list specifying how to rename the levels.

Details:

     For the factor replacement method, a 'NA' in 'value' causes that
     level to be removed from the levels and the elements formerly with
     that level to be replaced by 'NA'.

References:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

See Also:

     'nlevels', 'relevel', 'reorder'.

Examples:

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

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

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

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

     ## we can add levels this way:
     f <- factor(c("a","b"))
     levels(f) <- c("c", "a", "b")
     f

     f <- factor(c("a","b"))
     levels(f) <- list(C="C", A="a", B="b")
     f

