[R] can predict ignore rows with insufficient info
Prof Brian Ripley
ripley at stats.ox.ac.uk
Wed Sep 17 08:29:12 CEST 2003
On Tue, 16 Sep 2003, Peter Whiting wrote:
> On Tue, Sep 16, 2003 at 04:17:59PM -0400, Thomas W Blackwell wrote:
> > Peter -
> > Your subsequent email seems just right. You have to determine
> > ahead of time which rows can be estimated.
> It seems that predict removes rows with insufficient information
> (ie, if I replace "ALBANY" with NA and refactor everything works)
> - I wonder why it doesn't exhibit the same behavior when it
> encounters a new level - just eliminate the row and go on...
> Somewhat related: I had been assuming (incorrectly)
> that length(x) would equal length(const$days) after
> x<-predict(g,const) - this isn't the case if any of the rows of
> const don't contain enough info for the model. Those rows are
> eliminated - I'd have expected them to just be NAs in the result.
That depends on the setting of option na.action: the factory-fresh default
is na.omit, which is what you are seeing. As from R 1.8.0 it will use a
default of na.pass for predict.lm.
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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