Select and Save the points that have 3 neighbors exactly 1 unit of distance away.

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James Peach 2020-9-22

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关闭： MATLAB Answer Bot 2021-8-20

A.mat

I am trying to select and save points to an array. I want to get all the points that have 3 points exaclty 1 unit away. I have set up a matrix that contains all the distance values between the points, but I am struggling to get points that meet the criteria. My code below is below. Thanks in advance.

load('A.mat');
x = A(:, 1);
y = A(:, 2);
z = A(:, 3);
SizeofA = size(A,1);
dist1a = nan(numel(x)); 
proximity = 1;
for i = 1:SizeofA  
  for j = 1:(i-1) 
    dist1a(i,j) = sqrt((x(i)-x(j)).^2 + (y(i)-y(j)).^2 + (z(i)-z(j)).^2);
    dist1a(j,i) = dist1a(i,j);
  end
end
i2keep = min(dist1a) == proximity && histc(dist1a)> 1;
keep_x1 = x(i2keep);
keep_y1 = y(i2keep);
keep_z1 = z(i2keep);
B = [keep_x1, keep_y1, keep_z1];

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James Peach 2020-9-23

Id like to do something along the lines of this but by row instead of all at once.

https://www.mathworks.com/matlabcentral/answers/142281-count-the-number-of-times-a-value-occurs-in-a-specific-of-an-array

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Answer 1

sushanth govinahallisathyanarayana 2020-9-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/598129-select-and-save-the-points-that-have-3-neighbors-exactly-1-unit-of-distance-away#answer_498745

You could loop through the points and obtain a distance matrix dist

for i=1:size(A,1)

dist(:,i)=sum((A-A(i,:)).^2)

end

thr=1e-5; % example

dist_th=sum(abs(dist-1)<=thr);

% thresholding distances which are nearly exactly one, and finding the number of points that obey it for each point. The threshold of 1e-5 is so that points which are not exactly one unit away, but are 0.99999 units away will be included.

neighbour_pts=A(dist_th==3,:) % finds points that have 3 such neighbours

Hope this helps.

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James Peach 2020-9-23

I already have a distance matrix but I am trying to use logical statements to grab all the points that have 3 or more 1 values inside the rows.

Select and Save the points that have 3 neighbors exactly 1 unit of distance away.

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Select and Save the points that have 3 neighbors exactly 1 unit of distance away.

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