Subscript a Factorial Design Object

DESCRIPTION:

Subscript an object of class fac.design.

USAGE:

x[i, j, drop] 
x[i, j] <- value 
x[[i, j]] <- value 

DETAILS:

This is a method for the subscripting functions for objects inheriting from class "fac.design". See [.data.frame for the general behavior of this function.