Calculate mean of a matrix with different indices

Question

Dion Theunissen 2021-3-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/775372-calculate-mean-of-a-matrix-with-different-indices

评论： Bjorn Gustavsson 2021-3-17

采纳的回答： Bjorn Gustavsson

在 MATLAB Online 中打开

Hi,

I have a loop as below.

RCAr = []
for k = 1:length(RCA);  
...
...
afstand = thisData(1:a,1);
lengte = size(dx);
lengte = round(lengte);
for i = 1:lengte-1
    P1 = [dx(i), dy(i), dz(i)];    
    P2 = [dx(i+1), dy(i+1), dz(i+1)];
    angleradian(i) = acos((P2(2)-P1(2)) / norm(P2-P1));
    distance(i) = norm(P1 - P2);
     
end
angleradian2(:,1) = angleradian;
distance2(:,1) = distance;
    RCAr(:,k) = angleradian2; %this point is not working
    plot(afstand,angleradian2, '-')
    hold on
end

I want to make a matrix of k columns with all the angleradians. But the indices of angleradian does not have the same length. How can I fix this?

I want to calculate the mean of each row and stdev of each row of that matrix.

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Answer 1

Bjorn Gustavsson 2021-3-17

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/775372-calculate-mean-of-a-matrix-with-different-indices#answer_650027

在 MATLAB Online 中打开

So you effectively have different number of dx for each k? If so I'd do this something like this:

angleradian2 = nan([MaxNrRows,MaxNrCols]); % pre-allocate a nan-array with correct size
RCAr = angleradia2; % just make place for this one too
distance = RCAr;    % and this one,
afstand = RCAr;     % and this one...
for i1 = 1:length(RCA);  % Changed k to i1 to get identifying label on loop-variable
  ...
  ...
  afstand(i1,1:a) = thisData(1:a,1);
  lengte = size(dx,1); % or 2 instead of 1, size returns a 2 (at least) element array with
                       % [sz1, sz2, ... szN] since you use this as an upper
                       % bound of your iteration it should be a scalar!
  lengte = round(lengte);
  for i2 = 1:lengte-1  % changed i to i2 for same reason as above AND keep i free for complex unit
    P1 = [dx(i2), dy(i2), dz(i2)];    
    P2 = [dx(i2+1), dy(i2+1), dz(i2+1)];
    angleradian2(i1,i2) = acos((P2(2)-P1(2)) / norm(P2-P1));
    distance(i1,i2) = norm(P1 - P2);
    
  end
  RCAr(i1,:) = angleradian2(i1,:); %this point is not working
  plot(afstand,angleradian2, '-')
  hold on
  
end