R: Levels Attributes (original) (raw)
| levels {base} | R Documentation |
|---|
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.
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 thefactor 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
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 [factor](../../base/help/factor.html)s.
For the factor replacement method, a NA in valuecauses 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 vialevels(x) <- value is not the same as (and is preferred to)attr(x, "levels") <- value.
The replacement function is primitive.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)The New S Language. Wadsworth & Brooks/Cole.
See Also
[nlevels](../../base/help/nlevels.html), [relevel](../../stats/html/relevel.html), [reorder](../../stats/html/reorder.factor.html).
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, 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
[Package _base_ version 4.6.0 Index]