| terms.object {base} | R Documentation |
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:
factors |
A matrix of variables by terms showing which variables appear in which terms. The entries are 0 if the variable does not occur in the term, 1 if it does occur and should be coded by contrasts, and 2 if it occurs and should be coded via dummy variables for all levels (as when an intercept or lower-order term is missing). |
term.labels |
A character vector containing the labels for each of the terms in the model. Non-syntactic names will be quoted by backticks. |
variables |
A call to 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 |
The index of the variable (in variables) of the response (the left hand side of the formula). |
offset |
If the model contains offset terms there
is an offset attribute indicating which variables 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").
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.
Examples of the specials argument can be seen in the
aov and coxph functions.