I am still not convinced you have to transpose the matrix but maybe I am having an off-day, i.e. to blind to see it;-) When I read to your post the first thing that jumps into mind is the use of a database., especially since your "reduce functions" are simple.
However, assuming you insist on transposing, you might be able to speed things up. The case N != M is more difficult then N = M. The approach you take right now is the straightforward approach but this can give poor performance (as you have probably noticed).
In general: depending on circumstances, things like how much storage you have available and more importantly how M relates to N (|N-M| small or gcd(N,M) is not small) you can improve by using a more refined algorithm. (This I have taken from the Wiki, already suggested in my earlier response.) You can find pointers there to articles on the subject of in-place matrix transposition. I don’t know of any Perl implementations but the pointers on the Wiki also contain source code so you should be able to rewrite that into Perl if needed.
HTH, dHarry
In reply to Re^3: An efficient, scalable matrix transformation algorithm
by dHarry
in thread An efficient, scalable matrix transformation algorithm
by Luftkissenboot
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