I have a matrices (b1 and popx) with size 25000x50000, code is a vector which contains unique values in b1 (of length 300). For elements in popx which correspond to each unique value of b1, I need the sum of popx,
The below code takes very long (>2 hours) to operate, Any help to lower computation time is much appreciated
for i=1:300
popx1=popx;
popx1(b1~=code(i))=NaN;
popn=nansum(nansum(popx1));
popn1(i)=popn;
end;
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