How to calculate the sum of values in column 2 if column 1 has a certain value?

I have to analyze stock accounting. I have a large matrix (10000 x 2). In the first column I have the product code and in the second column I have the quantity taken from the storage. Every action has it's own row. How can I calculate the sum for every product?

I don't know how many product codes there are.

I have tried eg. arrayfun and to generate matrices with for loops and then the sum of the splitted matrices, but the results aren't right.

With this code I got the sum separately, but then I got stuck..

n = length(C)-1;

for i = 1:1:n

    if C(i,1)~= C(i+1,1)
        S = sum(B(i))

    end
end

Thank you in advance!

Answer 1

[Andrei Bobrov]

a - your array < 10000 x 2 double >

[a1,ii,ii] = unique(a(:,1));
out = [a1,accumarray(ii,a(:,2))];