[R] Ordering boxplot factors; thank you!

[Joseph LeBouton]

Profs. Ripley and Schwartz,

Thank you both very much for the suggestions!  These are exactly what I 
was looking for.  I'll re-read the boxplot help yet again; every time I 
read it something essential worms its way into my consciousness, but it 
enters more freely when I have a hint where to look.  The sad truth is 
that I was heading for a ~10-line hacker solution.  You've saved me from 
my usual code-writing ignomy.

Happy new year,

-Joseph

Prof Brian Ripley wrote:
> On Thu, 5 Jan 2006, Marc Schwartz wrote:
> 
>> On Thu, 2006-01-05 at 20:27 -0600, Joseph LeBouton wrote:
>>
>>> Hi all,
>>>
>>> what a great help list!  I hope someone can help me with this puzzle...
>>>
>>> I'm trying to find a simple way to do:
>>>
>>> boxplot(obs~factor)
>>>
>>> so that the factors are ordered left-to-right along the x-axis by
>>> median, not alphabetically by factor name.
> 
> 
> The thing to realize is that they are not alphabetic, but ordered by 
> factor levels.  So the key is to set the levels.  (The help page for 
> boxplot does say that, as I was relieved to find.)
> 
>>> Complicated ways abound, but I'm hoping for a magical one-liner that'll
>>> do the trick.
>>>
>>> Any suggestions would be treasured.
>>>
>>> Thanks,
>>>
>>> -jlb
>>
>>
>>
>> Using the first example in ?boxplot, which is:
>>
>> boxplot(count ~ spray, data = InsectSprays, col = "lightgray")
>>
>>
>>
>> Get the medians for 'count by spray' using tapply() and then sort the
>> results in increasing order, by median:
>>
>>  med <- sort(with(InsectSprays, tapply(count, spray, median)))
>>
>>> med
>>
>>   C    E    D    A    F    B
>> 1.5  3.0  5.0 14.0 15.0 16.5
>>
>>
>> Now do the boxplot, setting the factor levels in order by median:
>>
>>  boxplot(count ~ factor(spray, levels = names(med)),
>>          data = InsectSprays, col = "lightgray")
>>
>>
>> So...technically two lines of code.
> 
> 
> This was answered yesterday in terms of bwplot.  See ?reorder.factor
> for the same example done using reorder.factor.  That will give you the 
> single line asked for, and be self-explanatory.
> 

-- 
************************************
Joseph P. LeBouton
Forest Ecology PhD Candidate
Department of Forestry
Michigan State University
East Lansing, Michigan 48824

Office phone: 517-355-7744
email: lebouton at msu.edu