How to create a sliding window function?

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mejali 2015-10-17

3
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249070-how-to-create-a-sliding-window-function

评论： Pragati Patel 2022-3-29

I have a code called SampEn and would like to modify it to allow multiple calculations over a sliding window in the following fashion: 1. SampEn(data1:200) 2. SampEn(data(2:201) 3. SampEn(data(3:202) 4. and so on, moving one element forward each time until I reach the end of that data set (e.g. if 1000 elements, then the last analyzed set is data(801:1000).

The original code for SampEn is:

 function saen = SampEn(data)
 r = 0.2*std(data);
 N = length(data);
 correl = zeros(1,2);
 dataMat = zeros(2+1,N-2);
 for i = 1:2+1
    dataMat(i,:) = data(i:N-2+i-1);
 end
 for m = 2:2+1
    count = zeros(1,N-2);
    tempMat = dataMat(1:m,:); 
    for i = 1:N-m
        dist = max(abs(bsxfun(@minus,tempMat(:,i+1:N-2),tempMat(:,i))));
        D = (dist < r);
        count(i) = sum(D)/(N-2);
    end
    correl(m-2+1) = sum(count)/(N-2);
end
saen = log(correl(1)/correl(2));
end

There has to be a faster way to do this than manually having to type in each interval..and I can't wrap my brain around it..Thanks

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采纳的回答

Star Strider 2015-10-17

15
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249070-how-to-create-a-sliding-window-function#answer_196281

在 MATLAB Online 中打开

Assuming the length of ‘saen’ does not change between iterations, this is one (partially-tested because I did not run it with ‘SampEn’) way:

L = 1000;
w = 200;
for k1 = 1:L-w+1
    datawin(k1,:) = k1:k1+w-1;
    saen(k1,:) = SampEn(data(datawin(k1,:)));    
end

This saves the index ranges in the event you need them. If you don’t, eliminate the subscript references in ‘datawin’.

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mejali 2015-10-17

在 MATLAB Online 中打开

Ok I inserted it into the SampEn function:

 function saen = SampEn(data)
 r = 0.2*std(data);
 N = length(data);
 correl = zeros(1,2);
 dataMat = zeros(2+1,N-2);
 for i = 1:2+1
    dataMat(i,:) = data(i:N-2+i-1);
 end
 for m = 2:2+1
    count = zeros(1,N-2);
    tempMat = dataMat(1:m,:); 
    for i = 1:N-m
        dist = max(abs(bsxfun(@minus,tempMat(:,i+1:N-2),tempMat(:,i))));
        D = (dist < r);
        count(i) = sum(D)/(N-2);
    end
    correl(m-2+1) = sum(count)/(N-2);
end
saen = log(correl(1)/correl(2));
end
L = 1000;
w = 200;
for k1 = 1:L-w+1
    datawin(k1,:) = k1:k1+w-1;
    saen(k1,:) = SampEn(data(datawin(k1,:)));    
end

Then I attempt to run it for a row vector (I call it Interval) that consists of 1000 elements (each element represents a specific heart rate) by typing SampEn(Interval) in the command window. I get the following error reply:

 x=SampEn(Interval)
 Error: File: SampEn.m Line: 23 Column: 1
 This statement is not inside any function.
 (It follows the END that terminates the definition of the function    "SampEn".)

My goal is for it to return a row vector with calculation of SampEn for each window length; the row vector should have 801 elements if the window length is 200 and it moves forward by 1 each time up to 1000.

Thanks!!!!

Star Strider 2017-5-9

My pleasure!

I would appreciate a Vote for my Answer.

Pragati Patel 2022-3-29

@Star Strider Hi! My query is i want to calculate the feature i.e SampEn with a 200 bin sliding window and a 100 bin overlap; 1. SampEn(1:200) 2. SampEn(100:300) 3.SampEn(200:400) and so on. How shall i edit the code? Please respond.

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