| levels {base} | R Documentation |
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 assignment form ("levels<-") of levels is a generic
function and new methods can be written for it.
The most important method is that for factors:
levels(x) levels(x) <- value
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. |
For the factor assignment 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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
## 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