Bug in predict(newdata=x) with poly() (PR#1258)

predict.poly is easy. The problem (as for bs and ns) is getting it used by
predict.lm.  Thomas Yee (I think) has made a solution available, but the
consensus was that it could be done more elegantly at a lower level.  We
already preserve information on contrasts and sets of levels: we need to
preserve similar information for poly() and spline terms.

Yes, I didn't notice that predict.bs wasn't being called by
predict.lm.

I noticed this was still open last week, and put it on my (private) TODO
list.

A short-term workaround would be to put code like this into
predict.lm, at the point where tt contains the terms of the fit, and
it has been determined that newdata is not missing:

  if (any(c('poly','bs','ns') %in% flatten(tt)))          
     warning("newdata not supported with 'poly', 'ns', or 'bs'")

I don't know if there's already a function like flatten in R; here's a
simple one:

flatten <- function (expr) 
{
  if (is.expression(expr) | is.call(expr) | is.list(expr)) {
    unlist(lapply(as.list(expr), flatten))
  } else {
    as.character(expr)
  }
}

There may be other functions besides poly, bs and ns that return
bases; I don't know.

Duncan Murdoch
 


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