How to store values from a for loop and starting a new row after every 3rd iteration?

Hello, I am looking to populate a [65x3] matrix from a for loop where after every third itiration a new row will begin so that it looks something like this:

[3, 7, 9
11, 3, 4]

%This is my current code for storing values in a [65x3] matrix.
RARmat = zeros(65, 3)
for ii = 1:65
    RARatio = AUC/RA;
    disp(RARatio)
    % RAR Matrix
    RARmat(ii, :) = RARatio;
end

I recieved help to create this code in an earlier questions. In the comments I attempted to ask this as a follow up question if you would like to view it the link is here: https://www.mathworks.com/matlabcentral/answers/481516-store-values-from-a-for-loop-into-a-matrix

I would really appreciate any help with this. Thank you in advance!

Answer 1

[the cyclist]

RARmat = zeros(65, 3);
for ir = 1:65
    for ic = 1:3
        RARmat(ir,ic) = rand();
    end
end

The inner loop in this code works across the columns, and then after the third column is filled in, the inner loop is done. The outer loop works down the rows. Is that what you mean?

(I'm just filing in a random value in each element.)

[Jo E.]

That is perfect! Thank you so much!

[the cyclist]

Happy to help. For your awareness, though, one great aspect of MATLAB is the ability to write "vectorized" code. For example, the above code could have been written with only one for loop, like this:

RARmat = zeros(65, 3);
for ir = 1:65
    RARmat(ir,:) = rand(1,3);
end

or even with no for loops at all, like this:

RARmat = rand(65,3);

where you don't even need the preallocation step.

Of course, your ability to vectorize will be dependent on exactly what you need to fill in.