| attr {base} | R Documentation |
Object Attributes
Description
Get or set specific attributes of an object.
Usage
attr(x, which, exact = FALSE)
attr(x, which) <- value
Arguments
x |
an object whose attributes are to be accessed. |
which |
a non-empty character string specifying which attribute is to be accessed. |
exact |
logical: should |
value |
an object, the new value of the attribute, or |
Details
These functions provide access to a single attribute of an object. The replacement form causes the named attribute to take the value specified (or create a new attribute with the value given).
The extraction function first looks for an exact match to which
amongst the attributes of x, then (unless exact = TRUE)
a unique partial match.
(Setting options(warnPartialMatchAttr = TRUE) causes
partial matches to give warnings.)
The replacement function only uses exact matches.
Note that some attributes (namely class,
comment, dim, dimnames,
names, row.names and
tsp) are treated specially and have restrictions on
the values which can be set. (Note that this is not true of
levels which should be set for factors via the
levels replacement function.)
The extractor function allows (and does not match) empty and missing
values of which: the replacement function does not.
NULL objects cannot have attributes and attempting to
assign one by attr gives an error.
Both are primitive functions.
Value
For the extractor, the value of the attribute matched, or NULL
if no exact match is found and no or more than one partial match is found.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
Examples
# create a 2 by 5 matrix
x <- 1:10
attr(x,"dim") <- c(2, 5)