class(x)
class(x) <- value
unclass(x)
inherits(x, what, which = FALSE)
oldClass(x)
oldClass(x) <- value
value
can also be NULL
.class
as a character vector of length one and
method dispatch can happen on several arguments, instead of
only the first. However, S3 method selection attempts to treat objects
from an S4 class as if they had the appropriate S3 class attribute, as
does inherits
. Therefore, S3 methods can be defined for S4
classes. See the Classes and Methods
help pages for details. The replacement version of the function sets the class to the value
provided. For classes that have a formal definition, directly
replacing the class this way is strongly deprecated. The expression
as(object, value)
is the way to coerce an object to a
particular class. The analogue of inherits
for formal classes is
is
. The two functions behave consistently
with one exception: S4 classes can have conditional
inheritance, with an explicit test. In this case, is
will
test the condition, but inherits
ignores all conditional
superclasses. Many R objects have a class
attribute, a character vector
giving the names of the classes from which the object inherits.
If the object does not have a class attribute, it has an implicit
class, "matrix"
, "array"
or the result of
mode(x)
(except that integer vectors have implicit class
"integer"
). (Functions oldClass
and
oldClass<-
get and set the attribute, which can also be done
directly.)
When a generic function fun
is applied to an object with class
attribute c("first", "second")
, the system searches for a
function called fun.first
and, if it finds it, applies it to
the object. If no such function is found, a function called
fun.second
is tried. If no class name produces a suitable
function, the function fun.default
is used (if it exists). If
there is no class attribute, the implicit class is tried, then the
default method.
The function class
prints the vector of names of classes an
object inherits from. Correspondingly, class<-
sets the
classes an object inherits from. Assigning NULL
removes the
class attribute.
unclass
returns (a copy of) its argument with its class
attribute removed. (It is not allowed for objects which cannot be
copied, namely environments and external pointers.)
inherits
indicates whether its first argument inherits from any
of the classes specified in the what
argument. If which
is TRUE
then an integer vector of the same length as
what
is returned. Each element indicates the position in the
class(x)
matched by the element of what
; zero indicates
no match. If which
is FALSE
then TRUE
is
returned by inherits
if any of the names in what
match
with any class
.
All but inherits
are primitive functions.
UseMethod
, NextMethod
,
group generic, internal generic
x <- 10
class(x) # "numeric"
oldClass(x) # NULL
inherits(x, "a") #FALSE
class(x) <- c("a", "b")
inherits(x,"a") #TRUE
inherits(x, "a", TRUE) # 1
inherits(x, c("a", "b", "c"), TRUE) # 1 2 0
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