matlab concatenate vectors if cycle

Question

joo 2012-10-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/49857-matlab-concatenate-vectors-if-cycle

 distances = sqrt((x - max(x)).^2 + (y - max(y)).^2);
    [peaks, iPeaks] = findpeaks(distances);%to find out where the curve turns around
          for i = 1 : length(iPeaks)-1
                    iPeaks1 = iPeaks(i);
                    iPeaks2 = iPeaks(i+1)-1;%analyse of consecutive pair of peaks
                     %skip small noise peaks
                   if length(iPeaks1:iPeaks2)>=5 
                      xx=x(iPeaks1:iPeaks2)
                       yy=y(iPeaks1:iPeaks2)
                   end
                end
hello

i need to construct vectors xx and yy. The problem is that at each cycle the past xx and yy is deleted but i want the opposite. i want them to keep the past information and grow at each cycle. what can i do? and also i know i should preallocate xx and yy.

i appreciate any help. thank you very much.

**this is a possible solution. the problem here is i need to preallocate. but if i do it, the xx and yy keep the zeros and continue to grow 'with the zeros inside' and that is wrong

:

    distances = sqrt((x - max(x)).^2 + (y - max(y)).^2);
    [peaks, iPeaks] = findpeaks(distances);%to find out where the curve turns around
    xx=[];
    yy=[];
    for i = 1 : length(iPeaks)-1
            iPeaks1 = iPeaks(i);
            iPeaks2 = iPeaks(i+1)-1;%analyse of consecutive pair of peaks
             %skip small noise peaks
           if length(iPeaks1:iPeaks2)>=5 
              xx = [xx; x(iPeaks1:iPeaks2)];%''concatenate''(connect)
              yy = [yy; y(iPeaks1:iPeaks2)];
           end
    end

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Answer 1

Titus Edelhofer 2012-10-4

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在 MATLAB Online 中打开

Hi,

to grow the xx and yy you would write the following:

xx = [xx x(iPeaks1:iPeaks2)];

or

xx = [xx; x(iPeaks1:iPeaks2)];

depending on x being a row vector (first version) or a column vector (second). If you want to preallocate:

N = length(iPeaksNoise);
xx = zeros(N, 1);
yy = zeros(N,1);
counter = 0;
for i = 1 : length(iPeaksNoise)-1
     iPeaks1 = iPeaksNoise(i);
     iPeaks2 = iPeaks(i+1)-1;%analyse of consecutive pair of peaks
     %skip small noise peaks
     nPeaks = iPeaks2-iPeaks+1;
     if nPeaks>=5 
       xx(counter+(1:nPeaks)) = x(iPeaks1:iPeaks2);
       yy(counter+(1:nPeaks)) = y(iPeaks1:iPeaks2);
       counter = counter + nPeaks;
     end
end
xx(counter+1:end) = [];
yy(counter+1:end) = [];