| class {base} | R Documentation |
R possesses a simple generic function mechanism which can be used for an object-oriented style of programming. Method dispatch takes place based on the class of the first argument to the generic function.
class(x)
class(x) <- value
unclass(x)
inherits(x, what, which = FALSE)
oldClass(x)
oldClass(x) <- value
x |
a R object |
what, value |
a character vector naming classes. |
which |
logical affecting return value: see ‘Details’. |
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 a zero-length vector or
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.
An additional mechanism of formal classes is available in
packages methods which is attached by default. For objects
which have a formal class, its name is returned by class
as a character vector of length one.
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.
Functions oldClass and oldClass<- behave in the same way
as functions of those names in S-PLUS 5/6, but in R
UseMethod dispatches on the class as returned by
class (with some interpolated classes: see the link) rather
than oldClass. However, group generics dispatch
on the oldClass for efficiency, and internal generics
only dispatch on objects for which is.object is true.
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