How do I display only positive numbers from a matrix, i.e column 1 has to be positive to display the corresponding 3 columns of data?

I have column 1 which shows the index returns for each day, the next 3 columns are stock price returns from the corresponding day. There are currently days displaying a negative return for the index and the 3 stock prices next to it. I want to code that I only want to display the positive index returns and the corresponding stock prices of that same day.

[Christopher Wolfe]

The returns are denoted in this line rets = log(price(2:end,:)./price(1:end-1,:));

[Ive J]

A = [randi([-10 10], 4, 1), randi([20 100], 4, 3)]

A = 4×4

3 20 63 45 -6 20 45 45 -6 33 54 80 10 99 48 61

idx = A(:, 1)  > 0; % positive indices only
newA = A(idx, :)

newA = 2×4

3 20 63 45 10 99 48 61

Answer 1

[Walter Roberson]

mask = find(rets >= 0);
prets = rets(mask);
pprice = price(mask+1,:);

rets(K) is calculated based upon both price(K+1,:) and price(K,:) so it is not clear which of the two days you would want to have displayed. Here I chose to have it associated with the second day rather than the first.

[Christopher Wolfe]

I'm after the same row. So for example here are two lines of the data;

-0.00502163330810033 -0.00535602354270113 -0.00175905055456396 -0.00195122013126169

0.0191518806112861 0.0232968219264112 0.0157208477869482 0.0189597476631202

In this instance I only want to be showing the bottom row. To put it into context there's 1278 rows, basically just want to filter out all of the rows where the number in column 1 is a negative

[Christopher Wolfe]

Column 1 is the index return for that day

[Walter Roberson]

pprice = price(price(:,1)>=0, :);