[R] biplot with grouped observations

[Kim Milferstedt]

Hi,

I'd like to plot the results of PCA in biplots, grouping the 
observations by using different symbols. With xyplot in lattice I can 
easily differentiate the groups (see for example DAAG, p 285) but it 
seems difficult (or impossible?) to plot the vectors for the 
variables as well as xyplot cannot handle secondary axis very well. 
Using the basic plot I can combine observations and variables in one 
plot but cannot differentiate the groups of observations as easily as 
in xyplot. What could I do to get grouped observations in a biplot?

Thanks already,

Kim

__________________________________________

Kim Milferstedt
University of Illinois at Urbana-Champaign
Department of Civil and Environmental Engineering
4125 Newmark Civil Engineering Building
205 North Mathews Avenue MC 250
Urbana, IL 61801
USA
phone: (001) 217 333-9663
fax: (001) 217 333-6968
email: milferst at uiuc.edu
http://cee.uiuc.edu/research/morgenroth