R: Help Process the 'specials' Argument of the 'terms' Function.

untangle.specials {survival}

R Documentation

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.

Value

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.

Examples

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)

[Package survival version 3.8-3 Index]