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 `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.

`nlevels`, `relevel`, `reorder`.

### Examples

```## assign individual levels
x <- gl(2, 4, 8)
levels(x) <- "low"
levels(x) <- "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 Index]