[R] Boxplot not doing what I think it should

[Uwe Ligges]

On 24.02.2011 19:15, Greg Snow wrote:
> Look at ?quantile, especially the detail section on "type" and the second reference (and the see also section).  There are many different definitions of quantiles/quartiles and different functions use different versions.
>


Particularly ?boxplots points to ?boxplot.stats  and that points to 
Tukey's "original" ?fivenum.

Uwe Ligges




>> -----Original Message-----
>> > From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> > project.org] On Behalf Of Lewis Berman
>> > Sent: Thursday, February 24, 2011 8:38 AM
>> > To: r-help at R-project.org
>> > Subject: [R] Boxplot not doing what I think it should
>> >
>> > My box plot below is drawing its upper whisker all the way to the last
>> > point, instead of showing the point as an outlier. Am I
>> > misunderstanding, or is it a bug?
>> >
>> > Help(boxplot) states for the parameter "range" that "this determines
>> > how far the plot whiskers extend out from the box. If range is
>> > positive, the whiskers extend to the most extreme data point which is
>> > no more than range times the interquartile range from the box. A value
>> > of zero causes the whiskers to extend to the data extremes."
>> >
>> > To my understanding, the code below, which drew the boxplot, should
>> > have drawn the right-hand whisker only to 387 and shown 496 as an
>> > outlier point. But it didn't. Using a range of 1.3 does. Horizontal
>> > versus vertical does not matter.
>> >
>> > Also, the right edge of the box does not show the same 3rd Quartile as
>> > does "summary." Explain, please.
>> >
>> >
>>> > > sort(t5g24times)
>> > [1] 111 135 201 234 283 283 284 285 300 370 387 496
>>> > > summary(t5g24times)
>> >    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
>> >   111.0   225.8   283.5   280.8   317.5   496.0
>>> > > iqr <- 317.5 - 225.8
>>> > > iqr
>> > [1] 91.7
>>> > > 317.5 + 1.5 * iqr
>> > [1] 455.05
>>> > > pdf()
>>> > > boxplot(c(t5g24times), horizontal=1, range=1.5)
>> >
>> >
>> > R version info:
>> > platform       x86_64-apple-darwin9.8.0
>> > arch           x86_64
>> > os             darwin9.8.0
>> > system         x86_64, darwin9.8.0
>> > status
>> > major          2
>> > minor          12.0
>> > year           2010
>> > month          10
>> > day            15
>> > svn rev        53317
>> > language       R
>> > version.string R version 2.12.0 (2010-10-15)
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