I have two arrays of same size E x 1, let's call them Values and Labels. Values have real-valued data points, while Labels have integer-valued group labels for each data point, ranging from 1 to N. In my application E could be on the order of 1e6, while N is on the order of 1e5, so there are on average ~10 data points sharing the same group label.
I would like to generate the accumulated sum of values sharing the same group label. That is, I want to generate an N x 1 vector GroupSum where GroupSum(i) = sum(Values(Labels == i)). This will be done for many instances of (Values, Labels) combinations in an outer loop, so it is important to do this quickly. Therefore, I would like to find a faster alternative to
for i = 1:N
GroupSum(i) = sum(Values(Labels == i));
Any suggestions would be appreciated.
Thanks in advance.