The Null Object

Usage

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

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.

Examples

is.null(list())    # TRUE (not so in S)
is.null(integer(0))# F
is.null(logical(0))# F
as.null(list(a=1,b='c'))

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