(hopefully) simple array op

Regarding my last mail, I typed too soon.  Figure I can do

a<-array(c(a,b),dim=c(2,2,3))

Seems to work fine.  But I would like to hear other ideas if you have
any.  In particular, I am going to have to do this operation over and
over.  That last index "3" will have to increase by one every time.
Seems like it would make for nicer code if I didn't have to worry about
that.  Thanks again.