Question

I am a total beginner in MATLAB and I hope to find some help here. I have some model prediction results for 80 individuals alltogether in one large matrix. I need to extract the data for each individual from the big matrix, assign them in a new variable/matrix, do some extra calculations and then plot certain information as needed.

To do so, I am trying to write a script with a loop function but in a complicated, or maybe more accurately: in a primitive way!

Simplified Example:
My matrix is called: All_Indi_Data …. its dimension is: 600 rows x 21 columns

%Column 1: grouping variable (e.g., code or ID with values 1,2,3,4,5, etc.); 
%Column 2: independent var.;
%Column 3: t;
%Column 4: OBS;
%Column 5: PRED;



i= length (All_Indi_Data);

%% First Indi.
q=1;    % indicating the ID of the indi for which I want to extract the data
j=1;    % variable added to insure writing start from the first row

for r=1:i
if All_Indi_Data (r,1)==q
  Indi_1 (j,1:21) = All_Indi_Data (r,1:21)
  j=j+1
end

end

%% Second Indi.
q=q+1
j=1

for r=1:i
if All_Indi_Data (r,1)==q
   Indi_2 (j,1:21) = All_Indi_Data (r,1:21)
   j=j+1
end

end

.
.
.

1) My first question is: can I allocate these data in new variables (Indi_1, Indi_2, ect.) in a more simple way with or without the loop function?!!! I would appreciate your help a lot.

2) Is there any code or any way to plot these selected parts (according to the grouping variable, e.g. data for Indi_1) from the previously mentioned big matrix without wasting a lot of time and space (wto recopying the core part of the code again and again) for the script, and using the loop function?! in other words, I would like to detect – with loop function & the grouping variable- which values are of interest and then to plot them (e.g. data in colum 3 with data from column 4 for each individual, starting from the first to the last)?!

I hope that I described my problem clearly and hope to hear something from the expert guys 🙂 …

Thanks a lot in advance ..

Answer 1

Try the following code:

for idx=1:80
    pos=find(All_Indi_Data(:,1)==idx);
    eval(['Indi_' num2str(idx) '=All_Indi_Data(pos,:);']);
end

What I do is: in each iteration, I search for a value of the ID, indicated in the variable idx. Note that I do not use ´i´ as the name of a variable, because Matlab uses it and ´j´ and the imaginary unit for complex numbers and that could cause problems.

Then, using find I search for the position (or positions) of All_Indi_Data in which I can find the information of that individual. Now I have in the variable ´pos´ the indexes of the rows in which there is information for the individual of interest.

Finally, using eval I extract the data for each individual into a variable. Note that eval combined with a loop makes it easy to create lots of variables. I indicate the rows I want to extract with ´pos´ and, as I want all the columns, I use just ´:´ (you could use ´1:21´ too).

With another similar loop you can plot the information you want. For example:

for idx=1:80
        eval(['x=Indi_' num2str(idx) ';']); 
        % Now I have in X the information for this individual
        %Plot the columns of x I want
        plot(x(:, 3), x(:,4));
        pause; %stay here until a press a key

end