| levels | 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.
levels(x) levels(x) <- value
x |
an object, for example a factor. |
value |
A valid value for |
Both the extractor and replacement forms are generic and new methods
can be written for them. The most important method for the replacement
function is that for factors.
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.
Note that for a factor, replacing the levels via
levels(x) <- value is not the same as (and is preferred to)
attr(x, "levels") <- value.
The replacement function is primitive.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
nlevels, relevel, reorder.
## 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, labels = c("apple", "salad", "orange"))
z
levels(z) <- c("fruit", "veg", "fruit")
z
## same, using a named list
z <- gl(3, 2, 12, labels = c("apple", "salad", "orange"))
z
levels(z) <- list("fruit" = c("apple","orange"),
"veg" = "salad")
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
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