Question

I have 3 data sets, two with coordinates and one with data with the length of n with a loop I would assign the data in this way

MAT = zeros(m, n);  
for i = 1:n
    MAT(Z(i), X(i)) = MAT(Z(i), X(i)) + DATA(i);
end

I want to do it without a loop since what I am trying to do is something like:

MAT = zeros(m, n);
mn = size(MAT);
MAT(sub2ind(mn, Z, X)) = MAT(sub2ind(mn, Z, X)) + DATA;

Anyone has an idea how to make it properly and efficiently?

Cheers.

Answer 1

You should use the function accumarray, for example:
Let:

>> Z = [ 1 2 4 3 1];
>> X = [3 2 1 4 3];
>> D = [5 6 7 8 -10];
>> m = 4;n = 4;

Then we have:

>> MAT = accumarray([Z(:),X(:)],D(:),[m,n])
MAT =
     0     0    -5     0
     0     6     0     0
     0     0     0     8
     7     0     0     0