[R] what does this mean in R-1.8.1 release notes?

[Peter Dalgaard]

"Liaw, Andy" <andy_liaw at merck.com> writes:

> > From: Peter Dalgaard [mailto:p.dalgaard at biostat.ku.dk] 
> > 
> > John Christie <jc at or.psychology.dal.ca> writes:
> > 
> > > what does this mean in R-1.8.1 release notes?
> > > 
> > >      o	median() no longer `works' for odd-length 
> > factor variables.
> > 
> > The median has always been undefined for factors, but nevertheless
> > median() gave an answer. If the length was even, it would 
> > fail since it needed to average non-numeric values. This 
> > confused some and the answer you got for in the odd-length 
> > case was meaningless anyway (what's the median of three 
> > pears, four apples, and two bananas?). So now we check.
> 
> Why not just give an error if median is given an unordered factor?

That's what we do and didn't:

    if (is.factor(x) || mode(x) != "numeric")
        stop("need numeric data")

(also for ordered factors; it is not clear what to do if the median
sits between two levels in that case either.)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
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