sum a column depending on another column

Hi there,

I would like to sum values in a column where a criterion has been met in another column in a corresponding row of a matrix.

take the matrix:

xx  6  xx  1;
xx  9  xx  0;
xx  10 xx  1;

I want to sum the second column but only for rows where the fourth column is equal to one.

Hence, using the example, I would hope to have a solution of 16.

Any help with this simple problem is greatly appreciated.

James

Answer 1

[Andrei Bobrov]

out = sum(A(A(:,4)~=0,2))

Answer 2

[Conrad]

Something like this:

% Dummy data.
A =[ NaN 6  NaN 1;...
     NaN 9  NaN 0;... 
     NaN 10 NaN 1];

idx = A(:,4)==1;
s = sum(A(idx,2));