The Null Object

Description

NULL represents the null object in R. NULL is used mainly to represent the lists with zero length, and 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

Details

is.null is generic: you can write methods to handle specific classes of objects, see InternalMethods.

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))# F
is.null(logical(0))# F
as.null(list(a=1,b='c'))