I have a long vector of values say x=rand(1e5,1), and a long but shorter cellarray with indices to the elements of x. I just want to compute means or sums over the vector subsets using these indices. There is a variable number of indices in cells and the indices are exclusive within each cell but may not be exclusive among the cells i.e. different cells may contain the same indices. I am aware of the accumarray but I assumed it can work for mutually exclusive sets of indices i.e. each element is used only once in aggregation. Is there any faster way to do that than in a loop:
id=arrayfun(@(i) randperm(n, randi(n)), 1:round(n/10), 'UniformOutput',false)';
tic; y=zeros(size(id)); for i=1:numel(id) y(i)=mean(q(id{i})); end; t=toc
Cheers
