untangle.specials {survival} | R Documentation |
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.
untangle.specials(tt, special, order=1)
tt |
a |
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. |
a list with two components:
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. |
formula <- Surv(tt,ss) ~ x + z*strata(id)
tms <- terms(formula, specials="strata")
## the specials attribute
attr(tms, "specials")
## main effects
untangle.specials(tms, "strata")
## and interactions
untangle.specials(tms, "strata", order=1:2)