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, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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