MATLAB: Clever solution sought: Summing values from an array into a vector component given in a second array

Question

I have two arrays — an array of indices and an array of values, both are K x M. The index array has values between 1:M. Now I want to obtain the vector whose jth component is sum( valArray( indArray == j ) ).

Can you think of way to do this that beats the simple for loop solution? I have a couple of bsxfun solutions to do the ( indArray == j ) in one shot, but those don't beat the for loop. I also have a way to do this using a sparse array, but that doesn't beat the for loop either.

Here's code to set up the problem and find the answer using a for loop:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%NOTE: set M and K to be much larger for the real problem
M = 10;
K = 5; 
indArray = randi(M,[K M]);
valArray = rand([K M]);
result = zeros(M,1);
for ii = 1 : M * K
   temp = indArray(ii);
   result(temp) = result(temp) + valArray(ii);
end

Thanks for taking a look.

Answer 1

I think you are looking for accumarray.