terms.object              package:base              R Documentation

Description of Terms Objects

Description:

     An object of class `terms' holds information about a model. 
     Usually the model was specified in terms of a `formula' and that
     formula was used to determine the terms object.

     The object itself is simply the formula supplied to the call of
     `terms.formula'.  The object has a number of attributes and they
     are used to construct the model frame.

Value:

     An object with the following attributes: 

 factors: A matrix of variables by terms showing which variables appear
          in which terms.

term.labels: A character vector containing the labels for each of the
          terms in the model.

variables: A list of the variables in the model

intercept: Either 0, indicating no intercept is to be fit, or 1
          indicating that an intercept is to be fit.

   order: A vector of the same length as `term.labels' indicating the
          order of interaction for each term 

response: 

  offset: If the model contains `offset' terms there is an `offset'
          attribute indicating which terms are offsets

specials: If the `specials' argument was given to `terms.formula' there
          is a `specials' attribute, a list of vectors indicating the
          terms that contain these special functions.


     The object has class `c("terms", "formula")'.

Note:

     These objects are different from those found in S.  In particular
     there is no `formula' attribute, instead the object is itself a
     formula.  Thus, the mode of a terms object is different as well. 

     An example of the `specials' argument can be seen in the `aov'
     function.

See Also:

     `terms', `terms.default', `formula'.

