R/untangle.specials.R

In survival: Survival Analysis

#
# This function takes a terms object, and extracts some aspects
#  of it into a "nice" list.  It is simple an operation that
#  I do again and again in the modeling routines, so it was
#  made into a separate function
#
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, 'factors')
    fname <- dimnames(facs)
    ff <- apply(facs[spc,,drop=FALSE], 2, sum)
    list(vars= (fname[[1]])[spc], tvar = spc - attr(tt, "response"),
	     terms= seq(ff)[ff & match(attr(tt, 'order'), order, nomatch=0)])
    }