Help process the 'specials' argument of the terms function.
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.
|
Value
a list with two components:Examples
# This is code from within the coxph program, m is the data frame and TT
# the terms structure for the formula. We wish to exclude first order
# strata() terms from the final X matrix, and also to extract these terms
# to a second data frame
TT <- terms(formula, specials='strata')
temp <- untangle.specials(TT, 'strata')
if (length(temp$vars)) {
X <- model.matrix( TT[-temp$terms], m)
m.strat <- m[temp$vars]
}
else X <- model.matrix(TT, m)