How can I do to avoid using eval?

Hi! I'm modifying a code created with Matlab but I have a problem: I'd like to avoid using the eval function and at the same time create arrays that contain a variable number of elements.

For example, in this part of code

num_int = 3;
  for k = 1 : num_int
      eval(['m = length(I',num2str(k),')'])
  for i = 1 : m
      if count_vector(k) == 0
          eval(['ydata_low_',num2str(k),'(i,:) = [I',num2str(k),'_0(i) I',num2str(k),'_1(i) I',num2str(k),'_2(i) I',num2str(k),'_3(i) I',num2str(k),'_4(i)]']); 
          eval(['ydata_high_',num2str(k),'(i,:) = [I',num2str(k),'_5(i) I',num2str(k),'_6(i) I',num2str(k),'_7(i) I',num2str(k),'_8(i)]']);
      end
  end

I should create ydata_low and ydata_high, in function of k (that is num_int and is worth is 3).

In short, six arrays should be created: ydata_low_1, ydata_low_2, ydata_low_3, ydata_high_1, ydata_high_2 and ydata_high_3. The program already creates the variables to be introduced into the matrices (see attachment). I'd also like that variables from I_0 to I_4 are inserted in data_low and the variables from I_5 to I_8 are inserted in data_high.

Thank you!!

Answer 1

[Guillaume]

The code to fix is not the one you show unfortunately, It's the code before that which creates all these numbered I variables.

Do not create numbered variables. Matlab already has a way of storing together things with an index: matrices and cell arrays. Instead of all these Ix_y you should have a single I variable (and a better, more meaningful name wouldn't hurt) that is a cell array with I{1} a 3121x10 matrix, |I{2} a 3554x10 matrix, and I{3} and 3510x10 matrix (each made by horizontally concatenating [Ix, Ix_0, ..., Ix_9]. With that your correct code is trivial:

num_int = numel(I);  %no more hardcoded size
for k = 1:num_int
   if count_vector(k) == 0
       y_data_low{k} = I{k}(:, 2:5);
       y_data_high{k} = I{k}(:, 6:10);
   end
end

To be honest, there isn't even a need for y_data_low and y_data_high since it's simply I{k}(:, 2:5) and I{k}(:, 6:10) respectively.