It has to be done in a loop? You could put a nested loop in there and loop over r...
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EDIT
Here is one way to do it.
T = 1:5;
r = [1 1 1 3 4];
E = [3 3 2 2 5];
T = T + accumarray(r.',E.',[5 1]).'
But it might be slower than using a loop... In fact, since you say that T is 20,000 times longer than r, I would bet this was slower than a loop.
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EDIT2 The timings report...
Have a look for yourself. Of course some of the accumarray solution could be sped of if the r and E could be made column vectors, which would avoid the transposition, but I doubt that will be much faster...
function [] = accum_loop
T = 1:2e7;
rand('twister',33)
tic
for ii = 1:100
r = ceil(rand(1,1000)*2e7);
E = ceil(rand(1,1000)*10);
for jj = 1:length(r)
T(r(jj)) = T(r(jj)) + E(jj);
end
end
toc
T2 = 1:2e7;
rand('twister',33)
tic
for ii = 1:100
r = ceil(rand(1,1000)*2e7);
E = ceil(rand(1,1000)*10);
T2 = T2 + accumarray(r.',E.',[2e7 1]).' ;
% T2 = T2 + accumarray(r.',E.',[2e7 1],@sum,0,true).' ;
end
toc
isequal(T,T2)
I get, as it stands:
Elapsed time is 0.016339 seconds.
Elapsed time is 7.278608 seconds.
And with your modifications (function handles are slow!):
Elapsed time is 0.016107 seconds.
Elapsed time is 23.642409 seconds.
