[R] group mean, minus each row's value

[Casey Klofstad]

I used the following to assign each row the group average, where w is
the new group average variable, x is the variabale to be averaged, and
g is the nominal group indicator:

w <- ave(x,g)

Now I want to calculate the group average, but WITHOUT each row's
value of x. Is there an easy way to do this? I'm sure I'm missing
something obvious here, but for the life of me I can't figure it out.

Thanks!
-- 
Casey A. Klofstad
University of Miami
Department of Political Science
Coral Gables, FL

klofstad at gmail.com
http://moya.bus.miami.edu/~cklofstad