[R] determining the order in which points are plotted

[Mike Miller]

I make plenty of scatterplots, especially using scatterplot.matrix from 
library(car).  One thing I don't know how to do is determine which points 
are plotted last.  Sometimes I plot a large number of points for multiple 
groups represented by different colors.

I would like to guarantee that point that are far from the centroid for 
their group are plotted last.  This way they will be visible because they 
won't be buried under a pile of points from another group.

As it stands, it looks like scatterplot.matrix (and maybe other plotting 
functions) lay down a group at a time, in order, so that the first group 
is most likely to be buried under later groups.  I try to sort factor 
levels so that the biggest groups go first, and that helps a little, but 
it isn't the complete solution I'm looking for.

Thanks in advance.

Mike

--
Michael B. Miller, Ph.D.
Minnesota Center for Twin and Family Research
Department of Psychology
University of Minnesota