[R] Biplots

[Damon Wischik]

I want to plot biplots. I have seen the function biplot, but there are
some extra features I would like, that I do not know how to achieve.

1. My observations, and my variables, fall into groups. Is there a way to,
say, plot the observations in several different colours, according to
which group the observation falls into? Similarly with the variables? I am
used to the lattice idiom, in which one specifies groups= and
panel.groups=, but biplot is not (if I understand correctly) a lattice
function, and I don't know how to express what I want with the biplot
command. 

2. I would like to not plot arrows but instead plot axes for the
variables, as suggested by Gower & Hand (1996). Or, ideally, plot axis
lines which extend on either side of the origin, as far as the maximum and
minimum observed value for that variable.

Damon Wischik.