R: The Null Object

NULL {base} | R Documentation

## The Null Object

### Description

`NULL` represents the null object in R: it is a reserved word. `NULL` is often returned by expressions and functions whose value is undefined.

`as.null` ignores its argument and returns the value `NULL`.

`is.null` returns `TRUE` if its argument is `NULL` and `FALSE` otherwise.

### Usage

    NULL
    as.null(x, ...)
    is.null(x)

### Arguments

`x` | an object to be tested or coerced.
`...` | ignored.

### Details

`NULL` can be indexed (see Extract) in just about any syntactically legal way: whether is makes sense or not, the result is always `NULL`. Objects with value `NULL` can be changed by replacement operators and will be coerced to the type of the right-hand side.

`NULL` is also used as the empty pairlist.

### Note

`is.null` is a primitive function.

### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

### Examples

    is.null(list())     # FALSE (on purpose!)
    is.null(integer(0)) # FALSE
    is.null(logical(0)) # FALSE
    as.null(list(a = 1, b = "c"))

[Package base version 3.1.2 Index]