[R] Ordering in factors ...

Prof Brian D Ripley ripley at stats.ox.ac.uk
Fri Jun 28 11:03:10 CEST 2002

On Fri, 28 Jun 2002 j.logsdon at lancaster.ac.uk wrote:

> This is a trivial question probably buried in page 21 somewhere of An
> Idiot's Guide to R.
> In MASS(2) P26 for S-Plus you can write:
> ordered(income)<-c("Lo","Mid","Hi")
> but in R 1.5.0 you get the response to such an instruction:
> Error: couldn't find function "ordered<-"
> What's the fix to this?  I have a series of models where the factors as
> reported need re-ordering so that the glm reports the coefficients with
> respect to the correct level.  At the moment, while the solutions are
> identical, I actually have to do some arithmetic to show this.

There are scripts for MASS3 in the VR bundle, which give

income <- ordered(c("Mid","Hi","Lo","Mid","Lo","Hi","Lo"))

inc <- ordered(c("Mid","Hi","Lo","Mid","Lo","Hi","Lo"),
    levels = c("Lo", "Mid", "Hi"))

ordered factors in R are not quite the same as those in S.

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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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