NULL                  package:base                  R Documentation

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:

       x: an object to be tested or coerced.

     ...: ignored.

Examples:

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

