Itterate over array in steps of 120.

Hi guys, I am trying to figure out how I can itterate over 16800 rows in steps of 120. I.e. I want to loop over the first 120 rows and then loop over the next 120 rows etc. . Currently, the script only loops the first 120 rows, but I cannot get it to itterate over al the other rows in loops of 120. Is there anybody who can help me out? Thanks a lot in advance!!!

r=readmatrix('data_jong_edit.txt');
r(isnan(r(:,1)),:)=[];

empty = nan(16800,2);
r = [r empty];

u=unique(r(:,1));

count1 = 0;
count2 = 0;
    
    for k=1:120
    
        if r(k,9) == 1 
        
                count1 = count1 + 1;
                count2 = count2 + 1;
         
                r(k,12) = count1;
                r(k,13) = count2;

         elseif r(k,9) == -1
       
                count1 = count1;
                count2 = count2 + 1;
         
                r(k,12) = count1;
                r(k,13) = count2;
                
        elseif r(k,9) == 9999
       
                count1 = count1;
                count2 = count2;
         
                r(k,12) = count1;
                r(k,13) = count2;
                
        end 
    end 

[Image Analyst]

Why not just do

for k=1 : size(r, 1)

Answer 1

[Torsten]

r=readmatrix('data_jong_edit.txt');
r(isnan(r(:,1)),:)=[];
empty = nan(16800,2);
r = [r empty];
u=unique(r(:,1));

for k=1:size(r,1)
    
    if mod(k,120) == 1
        count1 = 0;
        count2 = 0;
    end
    
    if r(k,9) == 1 
        
        count1 = count1 + 1;
        count2 = count2 + 1;
        
        r(k,12) = count1;
        r(k,13) = count2;
        
    elseif r(k,9) == -1
        
        count1 = count1;
        count2 = count2 + 1;
        
        r(k,12) = count1;
        r(k,13) = count2;
        
    elseif r(k,9) == 9999
        
        count1 = count1;
        count2 = count2;
        
        r(k,12) = count1;
        r(k,13) = count2;
        
    end 
end 

[MadjeKoe]

oh my god thank u so much!!!!