NULL represents the null object in R: it is a reserved
NULL is often returned by expressions and functions
whose value is undefined.
as.null ignores its argument and returns the value
TRUE if its argument
1 2 3
an object to be tested or coerced.
NULL can be indexed (see Extract) in just about any
syntactically legal way: whether is makes sense or not, the result is
NULL. Objects with value
NULL can be changed by
replacement operators and will be coerced to the type of the
NULL is also used as the empty pairlist.
is.null is a primitive function.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
1 2 3 4