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Hi list! I have a large matrix which I'd like to partition into blocks and for each block I'd like to compute the mean. Following a example where each letter marks a block of the partition: a a a d g g a a a d g g a a a d g g b b b e h h b b b e h h c c c f i i I'm only interested in the resulting matrix of means. How can this be done efficiently?

dear helplist, my student has fifty trees, numbered one to fifty, and a vector recording which tree a certain possum slept in on 12 nights. R> c [1] 3 14 17 22 26 26 17 40 43 25 46 46 R> Thus it slept in tree #3 on Monday, then tree #14 on Tues, and so on. I wish to test the null hypothesis that the animal chooses trees randomly; try R> table(c) c 3 14 17 22 25 26 40 43 46 1 1