From maechler at stat.math.ethz.ch  Mon Nov  8 10:36:42 2004
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Mon Nov  8 10:36:50 2004
Subject: [Rd] boxplot() defaults {was "boxplot in extreme cases"}
In-Reply-To: <3A822319EB35174CA3714066D590DCD50994E29C@usrymx25.merck.com>
References: <3A822319EB35174CA3714066D590DCD50994E29C@usrymx25.merck.com>
Message-ID: <16783.15914.413329.766502@gargle.gargle.HOWL>


    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.

However,
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))),
           medlwd=3)

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).

Martin


> 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.


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