Working with structures, I cannot make an "if" work inside a "for" loop and cannot make "find peaks" work either; Any suggestions?

I am trying to work on vectors inside the structure (arrays), but when I have an if statement inside the for loop, it doesn't do what I am expecting it to. This is to remove the unwanted (pen-up) data in a drawing task, i.e., the threshold is 0.1.

Plus, I need to extract the corners of a drawing task data. i.e., we have asked subjects to draw some patterns for us like cubes and now I have to detect the corners of each drawing in order to compare it to the original pattern that we have (although the pattern is so big and I have problems matching them with the drawings) and analyse the tremor when drawing. What I was doing was plotting the graphs for each vector (I have x and y coordinates) to get the whole drawing and then I wanted to compare it to the original template using imshowpair (do we have any other ways of doing it that seems more reasonable to you?). But findpeak does not work either as I just need the corners that act as local maximums (I used the threshold to get only 4 maximums for cubes, etc.). I understand the code for this part is incomplete and I get errors, too (Attempted to access x(188); index out of bounds because numel(x)=13.); I just stopped as it was not doing what I wanted.

I have the simple code:

files = dir('.../controls/*.txt');
for k = 1:length(files)
  data{k} = load(fullfile('.../controls/', files(k).name), '-ascii');
      if data{k}(:,6) < 0.1
          data{k}(:,6) = 0;
      end
  data{k}(:,2) = data{k}(:,2) * 20.32;
  data{k}(:,3) = data{k}(:,3) * 15.24;
   % Rescaling the drawings to match the 
   % dimensions of the active area of
   % the tablet, which were 20.32 x 15.24 cm
  plot(data{1,k}(:,2));
  [pksx{k},locsx{k}] = findpeaks(data{1,k}(:,2),'MinPeakHeight',11);
  plot(data{1,k},data{1,k}(:,2),data{1,k}(locsx{k}),pksx{k},'or')
  plot(data{1,k}(:,3));
  [pksy{k},locsy{k}] = findpeaks(data{1,k}(:,3),'MinPeakHeight',11);
  plot(data{1,k},data{1,k}(:,3),data{1,k}(locsy{k}),pksy{k},'og')
end

[dpb]

Think you'll need to supply some data and perhaps figures to illustrate what you're expecting to do here...nobody can do anything with your code as is.

[Amir Dehsarvi]

I have now attached one of my data files.

Answer 1

[Walter Roberson]

Are you sure about

        if data{k}(:,6) < 0.1
          data{k}(:,6) = 0;
      end

That tests to see if all entries in column 6 are less than 0.1, and if so sets them all to 0, but if even one is judged to not be strictly less than 0.1, none of them are set to 0.

Perhaps you want

idx = data{k}(:,6) < 0.1;
data{k}(idx,6) = 0;

[Amir Dehsarvi]

Hello Walter and thank you so much for answering my question. Yes, as I explained, the "if" part was not doing anything at all. I corrected my code by adding what you suggested and it is working perfectly fine now. Walter, do you know how I can get the corners (peaks) by any chance? I need to basically save all the six corners as it is for a pentagon drawing task (there are six main peaks and valleys and I need to locate them on my data and compare the image to the template that I have).

[Walter Roberson]

I have not happened to use anything fancier than findpeaks()

[Amir Dehsarvi]

Brilliant. I thought the same, but for some reason I just get the error:

Attempted to access x(188); index out of bounds because numel(x)=13.

Error in findpeaks (line 51)
        maxAt(nmax) = x(k+1);

Error in Controls (line 44)
    [pksx{k},locsx{k}] = findpeaks(data{1,k}(:,2),'MinPeakHeight',10);

Here is the modified code:

files = dir('.../controls/*.txt');
for k = 1:length(files)
  data{k} = load(fullfile('.../controls/', files(k).name), '-ascii');
      % Locating the pen-up data
  idx = data{k}(:,6) < 0.1;
  data{k}(idx,6) = 0;
  data{k}(idx,2) = 0;
  data{k}(idx,3) = 0;
% I thought I should remove the x and y coordinates as well to make things easier for findpeaks() part.
    % Rescaling
    data{k}(:,2) = data{k}(:,2) * 20.32;
    data{k}(:,3) = data{k}(:,3) * 15.24;
    plot(data{1,k}(:,2));
    [pksx{k},locsx{k}] = findpeaks(data{1,k}(:,2),'MinPeakHeight',10);
    plot(data{1,k},data{1,k}(:,2),data{1,k}(locsx{k}),pksx{k},'or')
    plot(data{1,k}(:,3));
    [pksy{k},locsy{k}] = findpeaks(data{1,k}(:,3),'MinPeakHeight',10);
    plot(data{1,k},data{1,k}(:,3),data{1,k}(locsy{k}),pksy{k},'og')
end

[Walter Roberson]

Unfortunately I do not have the signal processing toolkit to have findpeaks(). But could I ask you to use

which -all findpeaks

to check to see whether you are accidentally getting some other findpeaks() ?

[Amir Dehsarvi]

/Applications/MATLAB_R2014a.app/toolbox/signal/signal/@dspdata/findpeaks.m % dspdata method

/Applications/MATLAB_R2014a.app/toolbox/signal/signal/findpeaks.m % Shadowed

[Walter Roberson]

That path looks okay.

Does the problem happen with the sample file you included, or with a different file?

[Amir Dehsarvi]

Yes, it happens with all the data files that I have...

[Walter Roberson]

Sorry, nothing is obvious to me. I would need the toolbox to test with.

[Amir Dehsarvi]

Thank you very much for helping anyway...please let me know if you had any other suggestions about this.