Improvement II
Promote the problem to a 2D computation
begin
ST := <## [Index2,Index1] S;
-- Construct Transpose of S
Count :=
+<<[1..n,1..n](>>[1,1..n]S = >>[1..n,1]ST);
-- Compare n^2 items, reduce
most := max<< S;-- Figure the best?
mode := max<<((most = Count)*S);
-- Isolate the mode
end;
Costs: 1 permute, 2 floods, 1 partial reduction, 2 full reductions, local computation