R/untangle.specials.R

In drm: Regression and association models for repeated categorical data

"untangle.specials" <-
function (tt, special, order = 1) 
{
    spc <- attr(tt, "specials")[[special]]
    if (length(spc) == 0) 
        return(list(vars = character(0), terms = numeric(0)))
    facs <- attr(tt, "factor")
    fname <- dimnames(facs)
    ff <- apply(facs[spc, , drop = FALSE], 2, sum)
    list(vars = (fname[[1]])[spc], terms = seq(ff)[ff & match(attr(tt, 
        "order"), order, nomatch = 0)])
}