[R] Two factors -> nurical data dependency analyzing

[Prof Brian Ripley]

On Sun, 19 Feb 2006, Evgeniy Kachalin wrote:

> Hello, dear R users.
>
> What is the easiest and the most visualli understandable way to analize
> dependency of numerical variable on two factors?

interaction.plot() is a good start.

> Is the
> boxplot(y~f1+f2) the good way? It seems that this formula does not work.

No, nor is it documented to: the help page is there to help you.  You need 
a single factor as the grouping, so make one via an interaction.
boxplot(y ~ f1:f2) should work.  E.g.

library(MASS)
boxplot(FL ~ sex:sp, data=crabs)

Another idea is to use lattice's bwplot.  E.g.

library(lattice)
bwplot(FL ~ sex | sp, data=crabs)


-- 
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)
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