How do I save for loop data from series of images? I am creating two polygons along the borders in a set of images. i want to save the polygon data for every loop. Currently it is overwriting and only saving the last loops data.

    % code
for k = t0:56
    [epi,xi,yi] = roipoly(echo(:,:,k)); %manually click along epicardial border;
    [endo,xi2,yi2] = roipoly(echo(:,:,k)); %manually click along endocardial border;
end 
figure; plot(xi,yi,'b'); 
hold on 
plot(xi,yi,'b+'); 
plot(xi2,yi2,'r');  
plot(xi2,yi2,'ro');

Answer 1

[Nick]

The easiest way to store something in MATLAB is to use arrays and index them using your loop index or a separate counter if your loop index is not a simple 1:X.

I am assuming you just want to store the data and access them separately after the loop. An easy solution is to use cell arrays.

% make cell arrays
xEpi = cell(1,numel(t0:56));
yEpi = cell(1,numel(t0:56));
xEndo = cell(1,numel(t0:56));
xEndo = cell(1,numel(t0:56));

 % loop through data, assuming t0 is not 1;
counter = 1;
for k = t0:56
    [~,xEpi{counter},yEpi{counter}] = roipoly(echo(:,:,k)); % u can use the tilda instead of a trash variable if you do not use epi or endo
    [~,xEndo{counter},yEndo{counter}] = roipoly(echo(:,:,k)); %manually click along endocardial border;
counter = counter + 1;
end

You could then plot them all like you did in your previous example but then using a for loop:

% plot them all on individual figures:
for ii = 1:numel(xEpi) % assuming the same number of Epi and Endo
  figure; 
  plot(xEpi{ii},yEpi{ii},'b', 'Marker', '+'); 
  hold on 
  plot(xEndo{ii},yEndo{ii},'r', 'Marker','o');  
end
% or plot them all on the same figure:
figure
for ii = 1:numel(xEpi)
  plot(xEpi{ii},yEpi{ii},'b', 'Marker', '+'); 
  if ii==1
     hold on 
  end
  plot(xEndo{ii},yEndo{ii},'r', 'Marker','o');  
end

[Danielle Wilson]

Thank you that was really helpful!