NULL | R Documentation |
NULL
represents the null object in R: it is a reserved
word. NULL
is often returned by expressions and functions
whose value is undefined.
NULL as.null(x, ...) is.null(x)
x |
an object to be tested or coerced. |
... |
ignored. |
NULL
can be indexed (see Extract) in just about any
syntactically legal way: whether it 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: see the
examples. Because pairlists are often promoted to lists, you may
encounter NULL
being promoted to an empty list.
Objects with value NULL
cannot have attributes as there is only
one null object: attempts to assign them are either an error
(attr
) or promote the object to an empty list with
attribute(s) (attributes
and structure
).
as.null
ignores its argument and returns NULL
.
is.null
returns TRUE
if its argument's value
is NULL
and FALSE
otherwise.
is.null
is a primitive function.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
is.null(list()) # FALSE (on purpose!) is.null(pairlist()) # TRUE is.null(integer(0)) # FALSE is.null(logical(0)) # FALSE as.null(list(a = 1, b = "c"))
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