Extract data between peaks

Question

jay yawson 2019-6-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/466321-extract-data-between-peaks

评论： Adam Danz 2019-6-11

straightLASER01.xlsx

Hello everyone, I would really appreciate help on solving this problem. I am trying to segment an emg data based on heelstrikes recorded from the accelerometer. I have used the peak to peak to find the location of the heelstrikes. The first peak, third and fifth peak belong to the right foot. The second, fourth,and sixth correspond to the left foot. I would like to extract the data between. Two heelstrikes of the same foot. For example I would like to write a for loop to extract the emg data from peak 1 to peak 3, then peak 3 to peak 5 till the last peak. Here's what I tried to do but it doesn't work. I have showed the extraction portion in the picture attached. Thanks in advance

if true
  % clear all
EMG = readmatrix('straightLASER01.xlsx','Sheet',1); %read emg data
ACC = readmatrix('straightLASER01.xlsx','Sheet',2); %read accleration data
[pks,locs] = findpeaks(ACC,'MinPeakDistance',1000); %find peaks 
 for p = 1:length(locs)
       first_strike = floor(locs(p,:));
       third_strike = floor(locs((p+2),:));
       acc = EMG1(first_strike:third_strike , p);
 end

end

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Answer 1

Adam Danz 2019-6-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/466321-extract-data-between-peaks#answer_378566

编辑：Adam Danz 2019-6-10

在 MATLAB Online 中打开

This segregates the EMG1 data by every 2 right-foot steps.

rightFootIdx = 1 : 2 : numel(locs); 
for i = 1:length(rightFootIdx)-1
    acc = EMG1(locs(rightFootIdx(i)):locs(rightFootIdx(i+1)), p);
    % ...
end

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Adam Danz 2019-6-11

编辑：Adam Danz 2019-6-11

在 MATLAB Online 中打开

You'll probably have to interpolate after the for-loop so that you know the maximum length within the cell array.

My proposal is to use interp1() to interpolate each element of the cell array so that each element has the same length as the maximum element. Here's what you can do (using fake data)

acc1 = {1:4,1:6,1:2,1:3,1:10,1:15,1:4};   %fake data
maxlen =  max(cellfun(@length,acc1));   %maximum length (=15)
% Option 1: for-loop (more intuitive and readable)
acc1Interp = cell(size(acc1)); 
for j = 1:numel(acc1)
    acc1Interp{j} = interp1(1:numel(acc1{j}), acc1{j}, linspace(1,numel(acc1{j}),maxlen));
end
% Option 2: for those who don't like loops
acc1Interp2 = cellfun(@(x)interp1(1:numel(x), x, linspace(1,numel(x),maxlen)),acc1Interp,'UniformOutput',false);

Note that the elements of the cell array will all have the same number of data points but if those data were collected at a fixed interval of time, each element will now have a different sample rate.

Also note that if any of the elements in your array contain only 1 data point, the interp1() function will break. If that happens, write a conditional that either skips that cell array or replicates the single value to the maxlen.

jay yawson 2019-6-11

编辑：Adam Danz 2019-6-11

Concerning the same work, I've asked a similar question. I would like to extract the data between two regions. However these two regions are not the peaks and I don't know how to automatically detect that. Do you have any ideas? Kindly take a look if you manage to get some free time off you busy schedule. Many thanks.

https://www.mathworks.com/matlabcentral/answers/466441-extract-and-save-data-between-two-regions

Adam Danz 2019-6-11

I gave it a shot.

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Extract data between peaks

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