seemsS4Object {methods} | R Documentation |
Returns TRUE
if object
seems to have been generated from a formally defined (“S4”) class.
seemsS4Object(object)
object |
Any object. |
The class()
of the object is examined for the "package"
attribute included when objects are generated from an S4 class.
This test can be fooled in at least two ways:
TRUE
incorrectly if someone puts a "package"
string attribute on the class of an S3 object. Presumably unlikely.
FALSE
incorrectly for class definitions and certain other objects for packages that have not been INSTALL
ed since the seemsS4Object
was added to R. See the warning below.
Always TRUE
or FALSE
for any object.
One motivation for this function is to prevent standard S3 vector operations from being applied to S4 objects that are not vectors. Note that seemsS4Object()
alone is not that test. One also needs to check that the object does not inherit from class "vector"
. See the examples.
The existence of a class definition for the object's class is also not equivalent.
S4 class definitions are recorded for S3 classes registered via setOldClass
, but registering does not change the class of such objects, so they are not judged to be S4 objects (and should not be).
Certain other S4 objects used to be generated without the "package"
attribute in earlier builds of R, notably class definitions.
Packages using S4 objects must be reinstalled with a version of R recent enough to contain the seemsS4Object
function (e.g., the released R 2.3).
seemsS4Object(1) # FALSE seemsS4Object(getClass(class(1))) #TRUE ## how to test for an S4 object that is not a vector S4NotVector <- function(object) seemsS4Object(object) && !is(object, "vector") setClass("classNotNumeric", representation(x="numeric", y="numeric")) setClass("classWithNumeric", representation(y="numeric"), contains = "numeric") obj1 <- new("classNotNumeric", x=1, y=2) obj2 <- new("classWithNumeric", 1, y=2) seemsS4Object(obj1); seemsS4Object(obj2) # TRUE, TRUE S4NotVector(obj1); S4NotVector(obj2) # TRUE, FALSE