apply() question

what I want is the equivalent of

R> rbind(a[[1]],a[[2]],a[[3]],a[[4]],a[[5]])

Note that while do.call("rbind",a) is the natural solution it may in fact
be faster to create a matrix and use a loop to put things in it.

rval<-matrix(ncol=4, nrow=sum(sapply(a,nrow)))
i<-1
for(ai in a){
	r<-nrow(ai)
	rval[i+1:r,]<-ai
	i<- i+r
}


	-thomas