[R] terms.formula

[Roger Koenker]

I'm in the very initial stage of expanding the formula processing
in my quantile regression function rq() to handle additive
nonparametric components, say qss(x), or qss(x,z).  I need some
advice about strategy for formula processing.  My initial foray
was to use:

	terms(formula,specials="qss")

and then modify the components of the resulting
terms.object.  But in changing formula at factors to drop the qss
columns and rows, I ran afoul of methodsPackageMetaName
which claimed that it was "being abused" by this.

	if(!is.null(attr(formula,"specials"))){
		qss.col <- pmatch("qss",attr(formula,"term.labels"))
        	qss.row <- formula at specials$qss
        	formula at factors <- formula at factors[-qss.row,-qss.col,drop=FALSE]
        	}

My eventual objective is to be able to  make the model.matrix
corresponding to the linear, parametric part of the formula specified,
and then to cbind additional columns corresponding to the
nonparametric components and pass the whole thing to rq.fit.xxx,
where estimation will be handled.  So the essential question at
this point is:  how should I go about stripping off the qss
components for subsequent use.


url:	www.econ.uiuc.edu	Roger Koenker		Dept. of Economics UCL,
email	rkoenker at uiuc.edu	Department of Economics Drayton House,
vox: 	217-333-4558		University of Illinois	30 Gorden St,
fax:   	217-244-6678		Champaign, IL 61820	London,WC1H 0AX, UK
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