On Wed, 2009-08-19 at 13:49 -0700, Bert Gunter wrote:
Rolf:
Not sure what "reasonably thorough" means but:
? boxplot says:
Exactly Bert, the info is there is you want to look and do so hard
enough. However, it is perhaps expecting quite a lot of a new useR to
put this together from ?boxplot or ?bxp, and ?boxplot.stats.
Criticising correct, if cryptic or highlevel, responses to a list
where
people give their time for free, *and* not provide a more complete
solution is unfair, Rolf. The OP is free to respond and ask for
additional help once they've given it a go if they are still having
trouble..
One solution, if you are prepared to bastardise the standard
interpretation of the boxplot, is to compute the relevant boxplot
statistics using boxplot.stats and alter argument 'coef' to some
larger
multiple of the box height to represent "extreme" outliers, whatever
those might be. So here's the rope, try not to hang yourself
'Rnewbie'!
set.seed(1234)
dat <- rt(100, df = 2)
bxp1 <- boxplot.stats(dat)
bxp2 <- boxplot.stats(dat, coef = 2)
##Then you'd need to plot the boxplot without outliers
boxplot(dat, outpch = NA)
##Then plot the points 1.5-2 x box height
want <- bxp1$out %in% bxp2$out
out <- bxp1$out
out[want] <- NA
points(rep(1, length(out)), out, pch = 1, col = "blue")
##Then the further outliers
outout <- bxp2$out
points(rep(1, length(outout)), outout, pch = 2, col = "red")
How one decides what is an outlier or an extreme outlier is another
matter...? By chance the dummy data here shows one problem; there
isn't
much difference between 'outliers' and 'extreme outliers' towards the
bottom of the resulting plot so why should we distinguish them?
(By the way 'Rnewbie', this isn't something I recommend you do,
but you
might know more about your real world use case than I.)
HTH
G
Ps; is there a reason why you post anonymously, 'Rnewbie'? Do you not
want us to know who you are, but want our help?
...
pars a list of (potentially many) more graphical parameters,
e.g., boxwex
or outpch; these are passed to bxp (if plot is true); for
details, see
there.
Well, that seems pretty clear to me, so I went to ?bxp to find in
the pars
listing:
outlty, outlwd, outpch, outcex, outcol, outbg:
outlier line type, line width, point character, point size
expansion, color,
and background color. The default outlty= "blank" suppresses the
lines and
outpch=NA suppresses points.
It seems to me that this (and other omitted excerpts + examples)
is at least
a reasonable answer to the query (allowing the reader to at least
infer that
bxp does not distinguish degrees of outlyingness), so I don't
understand
your criticism. Feel free to respond privately if you prefer.
-- Bert
Bert Gunter
Genentech Nonclinical Biostatisics
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] On
Behalf Of Rolf Turner
Sent: Wednesday, August 19, 2009 1:27 PM
To: ottorino-luca.pant...@unifi.it
Cc: Rnewbie; ERRE
Subject: Re: [R] mild and extreme outliers in boxplot
On 20/08/2009, at 3:13 AM, Ottorino-Luca Pantani wrote:
Rnewbie ha scritto:
dear all,
could somebody tell me how I can plot mild outliers as a circle(°)
and
extreme outliers as an asterisk(*) in a box-whisker plot?
Thanks very much in advance
?boxplot
or
help(bxp)
This is the sort of response that gives R-help a bad name.
I had a reasonably thorough look at these help files and saw
***nothing***
that would answer the OP's question. The information may be there
--- I'm
not sure about this --- but it is far from obvious. Explicit
reference
to the appropriate lines of the help file(s) would be useful.
cheers,
Rolf Turner
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