as {methods}R Documentation

Force an Object to Belong to a Class


Coerce an object to a given class.


as(object, Class, strict=TRUE, ext)

as(object, Class) <- value



any R object.


the name of the class to which object should be coerced.


logical flag. If TRUE, the returned object must be strictly from the target class (unless that class is a virtual class, in which case the object will be from the closest actual class, in particular the original object, if that class extends the virtual class directly).

If strict = FALSE, any simple extension of the target class will be returned, without further change. A simple extension is, roughly, one that just adds slots to an existing class.


The value to use to modify object (see the discussion below). You should supply an object with class Class; some coercion is done, but you're unwise to rely on it.


an optional object defining how Class is extended by the class of the object (as returned by possibleExtends). This argument is used internally; do not use it directly.


as(object) returns the version of this object coerced to be the given Class. When used in the replacement form on the left of an assignment, the portion of the object corresponding to Class is replaced by value.

The operation of as() in either form depends on the definition of coerce methods. Methods are defined automatically when the two classes are related by inheritance; that is, when one of the classes is a subclass of the other.

Coerce methods are also predefined for basic classes (including all the types of vectors, functions and a few others).

Beyond these two sources of methods, further methods are defined by calls to the setAs function. See that documentation also for details of how coerce methods work. Use showMethods(coerce) for a list of all currently defined methods, as in the example below.

Basic Coercion Methods

Methods are pre-defined for coercing any object to one of the basic datatypes. For example, as(x, "numeric") uses the existing as.numeric function. These and all other existing methods can be listed as shown in the example.


Chambers, John M. (2016) Extending R, Chapman & Hall. (Chapters 9 and 10.)

See Also

If you think of using try(as(x, cl)), consider canCoerce(x, cl) instead.


## Show all the existing methods for as()

[Package methods version 3.6.0 Index]