[R] Boxplot across levels of a factor

[Prof Brian Ripley]

On Tue, 24 Aug 2004, Paul Boutros wrote:

> Hello,
> 
> I have a data-frame in which one-column is a factor:
> 
> > str(data);
> `data.frame':   194 obs. of  8 variables:
>  $ Type         : Factor w/ 3 levels "Nuclear-Rec..",..: 1 2 2 2 2 2 2 2 2 2
> ...
>  $ Locus        : num  0.000571 0.004000 0.001429 0.004857 0.007429 ...
> 
> And I'd like to make a boxplot of the data$Locus values, where each level of
> the factor gets its own box-and-whiskers plot.  I'm weak in R, but I thought
> there might be some shortcut to automating this instead of just creating a
> new data-structure with all the separate values?

There are two.  The simpler is

	boxplot(Locus ~ Type, data=data)

and you can also use

	with(data, boxplot(split(Locus, Type)))

(split() does automate the construction of a suitable data structure.)

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595