MATLAB: How to sum specific matrix elements

Question

Hello everyone,

i have a 10×2 matrix. i want to sum all the elements in the first column while the second column has the negative values. for the example matrix below,

i want a b matrix that gives me 2+4+4 result. (2,4 and 4 are the first column numbers which has negative numbers in the second column)

A=[2 -3;4 -4;5 3;4 -2;5 4;1 3];

I hope you can help me, thank you all!!!

Answer 1

Try this:

rowsToSum = A(:, 2) < 0;
theSum = sum(A(rowsToSum, 1)); % Sum first column where second column is negative.