[R] plot and factors

Jason Miller millerj at truman.edu
Fri Dec 2 13:40:48 CET 2005

Read R-helpers,

I'm relatively new to R and trying to jump in feet first.  I've been  
able to learn a lot from on-line and printed documentation, but  
here's one question to which I can't find an answer.  Well, it's a  
question with a couple parts.  Thanks in advance for any direction  
(partial or complete) that anyone can provide.

I have a data frame with three columns: Year, Semester, value1.  I  
want to treat Year and Semester as factors; there are many years, and  
there are three semesters (Fall, Spring, Summer).

First, I would like to be able to plot the data in this frame as Year  
v. value with one curve for each factor.  I have been unable to do  
this.  Is there any built-in R functionality that makes this easy, or  
do I need to build this by hand (e.g., using the techniques in FAQ  
5.11 or 5.29)?

Second, I would like to be able to plot the values against a doubly  
labeled axis that uses Year and Semester (three Semester ticks per  
Year).  Is there a relatively straightforward way to do this?   
(What's happening, of course, is that I'd like to treat Year+Semester  
as a single factor for the purpose of marking the axis, but I'm not  
sure how to do that, either.)

Again, thanks for whatever pointers people can share.


Jason E. Miller, Ph.D.
Associate Professor of Mathematics
Truman State University
Kirksville, MO

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