Re: [Matplotlib-users] Setting the whisker range for box plots

[Derek H. <DH...@cs...>]

I'd be happy to be shown wrong, but it seems the current
incarnation of boxplot cannot do this.  
 
The current syntax is:
 
boxplot(x, notch=0, sym='+', vert=1, whis=1.5,
        positions=None, widths=None)
 
What it *could* have to support what is needed is
an extra parameter:

boxplot(x, notch=0, sym='+', vert=1, whis=1.5,
        positions=None, widths=None, percentile=False)

When percentile=True, then the program would treat 
the value of whis as a percentile value (0.001 to 100) and
plot the whiskers and outliers accordingly.

For reference, please see:
http://en.wikipedia.org/wiki/Box-and-whisker_plot 
and the section that says:
"There are alternative implementations of this detail of the 
box plot in various software packages, such as the whiskers 
extending to at most the 5th and 95th (or some more extreme) 
percentiles"

and for examples of such an implementation:
http://www.originlab.com/index.aspx?s=8&lm=214&pid=959
or
http://ploticus.sourceforge.net/doc/rangebar.html 
(see the option called "tailmode" which allows switching
between 5th and 95th percentile, min and max, or 1.5 x IQR.)

Thanks
Derek


>>> "Derek Hohls" <DH...@cs...> 2007/01/23 03:29 PM >>>

I would like to have the extreme end of the upper whisker
on the box plot co-incide with the 98% of the data.

According to the documents:
whis (default 1.5) defines the length of the whiskers as        
a function of the inner quartile range.  They extend to the        
most extreme data point within ( whis*(75%-25%) ) data range.

So, in theory, a value of whis=1.9 should be what is needed
but this seems to produce a much lower point - what value 
do I need to use?

Thanks
Derek


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