R: Levels Attributes

levels {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 factors:

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.

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

[Package base version 2.5.0 ]