untangle.specials: Help Process the `specials' Argument of the `terms' Function.
Description
Given a terms structure and a desired special name, this returns an
index appropriate for subscripting the terms structure and another
appropriate for the data frame.
Usage
untangle.specials(tt, special, order=1)
Arguments
tt
a terms object.
special
the name of a special function, presumably used in the terms object.
order
the order of the desired terms. If set to 2, interactions with the special
function will be included.
vars
a vector of variable names, as would be found in the data frame, of the
specials.
terms
a numeric vector, suitable for subscripting the terms structure, that indexes
the terms in the expanded model formula which involve the special.