inherits
Test Inheritance of an Object
Description
Returns a logical value or an integer vector indicating from which classes 
x inherits. 
Usage
inherits(x, what, which = FALSE)
Arguments
| x | any object, possibly but not necessarily having a class attribute. | 
| what | a character vector of possible classes. | 
| which | logical flag: if TRUE, specify which classes matched the object; if FALSE, 
just say whether any classes matched the object. | 
 
Value
if which is FALSE, a single logical value. The value is TRUE if any  
of the classes in the class 
attribute of x match (exactly) any of the strings in what. 
if which is TRUE, an integer vector of the same length as what 
that contains the position in the class of x that each value in what 
matches. 
A zero is returned for elements of what that dont match any element of the 
class. 
See Also
Examples
# the definition of as.factor 
function(x) if(inherits(x,"factor")) x else factor(x) 
inherits(y~x, c("formula", "terms"))