How to make a counter in a for loop?

Hi.

I have a 330x7 matrix, and want to access every 10th row from 1:7.

My code looks like this, but I get error whatever I try.

 patient = 33;        
 k = 10;

 for i = 1:patient
    joint7(i,:) = main(10,1:7+k);
    k = k+10;
 end

What am I doing wrong?

Answer 1

[Akira Agata]

You can extract every 10th row of the matrix much easier, like:

% Assuming your 330x7 matrix
main = rand(330,7);

% Extract every 10th row
joint7 = main(10:10:end,:);

Answer 2

[umichguy84]

When using a for loop you don't have to step by 1, you can step by any number.

So while this would fix your issue:

 patient = 33;        
 k = 10;

 for i = 1:patient
    joint7(i,:) = main(k*i,1:7);
 end

An alternative is:

patient = 33;   
k=10;
joint7 = nan(patient,7); % It's faster if you prepopulate
i=1;
 for k = 10:k:length(main)
    joint7(i,:) = main(k,1:7);
    i = i + 1;
 end

Either will work, but I wanted to provide an alternative way of doing it.