[Rd] boxplot() defaults {was "boxplot in extreme cases"}

Martin Maechler maechler at stat.math.ethz.ch
Mon Nov 8 10:36:42 CET 2004

    AndyL> Try:

    AndyL> x <- list(x1=rep(c(0,1,2),c(10,20,40)), x2=rep(c(0,1,2),c(10,40,20)))
    AndyL> boxplot(x, pars=list(medpch=20, medcex=3))

    AndyL> (Cf ?bxp, pointed to from ?boxplot.)

Good! Thank you, Andy.

this is not the first time it had crossed my mind that R's
default settings of drawing boxplot()s are not quite ok -- and
that's why I've diverted to R-devel.

Keeping Tufte's considerations in mind, (and me not really wanting
to follow S-plus), shouldn't we consider to slightly change R's
boxplot()ing such that

   boxplot(list(x1=rep(c(0,1,2),c(10,20,40)), x2=rep(c(0,1,2),c(10,40,20))))

will *not* give too identically looking boxplots?
Also, the median should be emphasized more by default anyway.
{The lattice function  bwplot() does it by only drawing a large
 black ball as in Andy's example (and not drawing a line at all)}

One possibility I'd see is to use a default 'medlwd = 3'
either in boxplot() or in bxp(.) and hence, what you currently get by

   boxplot(list(x1=rep(c(0,1,2),c(10,20,40)), x2=rep(c(0,1,2),c(10,40,20))),

would become the default plotting in boxplot().
Of course a smaller value "medlwd=2" would work too, but I'd
prefer a bit more (3).


> From: Erich Neuwirth
> I noticed the following:
> the 2 datasets
> rep(c(0,1,2),c(10,20,40)) and
> rep(c(0,1,2),c(10,40,20))
> produce identical boxplots despite the fact that the medians are 
> different. The reason is that the median in one case 
> coincides with the
> first quartile, and in the second case with the third quartile.
> Is there a recommended way of displaying the median visibly in these 
> cases? Setting notch=TRUE displays the median, but does look strange.

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