Findpeaks and maxk without sorting

Dear all,

The 'Pilant_Vy_envR' (xlsx) file is of these dimensions: 1200x600. Every column is a signal, and i would like to find the three main peaks (non sorted) in every column. I'm stuck with the following code:

ncolVy=size(Pilant_Vy_envR,2);  
max = zeros(ncolVy,3) ; 
for l = 1:ncolVy
  [PKSVy,locs] = findpeaks(Pilant_Vy_envR(:,l)); 
  maxvy(l,:) = maxk(PKSVy,3);
  MaxVy = maxvy.';
end

The output contain 3x600 columns. Three are the maxima obtained by every signal, but the code above sort them. I would like infact to obtain the peaks as they are in the graph.

So for example for the first signal (first column) i would like the peaks with their order:

But with maxk i have the peaks with the order:1-3-2.

Can someone help me?

Best regards.

Answer 1

[Voss]

% a smaller example:
Pilant_Vy_envR = zeros(13,2);
Pilant_Vy_envR(2:3:end,1) = [30; 15; 10; 20];
Pilant_Vy_envR(3:3:end,2) = [25; 17; 32; 16];

% 2 signals with 4 peaks each
disp(Pilant_Vy_envR)

     0     0
    30     0
     0    25
     0     0
    15     0
     0    17
     0     0
    10     0
     0    32
     0     0
    20     0
     0    16
     0     0

% number of columns/signals
ncolVy = size(Pilant_Vy_envR,2);

% (initialize MaxVy with its right size)
MaxVy = zeros(3,ncolVy);

for col = 1:ncolVy
    
    % first, find all the peaks (don't need the locations "locs" for this)
    PKSVy = findpeaks(Pilant_Vy_envR(:,col));
    
    % use the 2nd output of maxk, which is the indices of the 3 highest peaks
    [three_peaks,idx] = maxk(PKSVy,3);
    
    % sort those indices, and use the second output from sort, which is
    % their order when sorted
    [~,jj] = sort(idx);
    
    % put the 3 highest peaks in the same order
    MaxVy(:,col) = three_peaks(jj);
    
end

disp(MaxVy);

    30    25
    15    17
    20    32

[Mattia Fattori]

Dear Voss,

now understand my mistakes, and the problem seems to be solved.

Thanks a lot for your help!

[Voss]

You're welcome!