On Wed, 30 Mar 2011, Terry Therneau wrote:
> I'm working on predict.survreg and am confused about xlevels.
> The model.frame method has the argument, but none of the standard
> methods (model.frame.lm, model.frame.glm) appear to make use of it.
But I see this in predict.lm:
m <- model.frame(Terms, newdata, na.action = na.action,
xlev = object$xlevels)
It is used to remap levels in newdata to those used in the fit.
>
> The documentation for model.matrix states:
> xlev: to be used as argument of model.frame if data has no
"terms"
> attribute.
Well, the code says
if (is.null(attr(data, "terms")))
data <- model.frame(object, data, xlev=xlev)
> But the terms attribute has no xlevels information in it, so I find this
> statement completely confusing. Any insight is appreciated.
It means exactly what it says: a 'data' argument with a terms
attribute is considered to be a model frame.
>
> Terry Therneau
>
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--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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