Find neighboring nodes in a list of node positions

Question

Raldi 2018-3-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/387118-find-neighboring-nodes-in-a-list-of-node-positions

回答： Image Analyst 2018-3-9

I have two vectors of X and Y positions

x = randn(10,1);
y = randn(10,1);

So x(1) with y(1) together make the position of node 1

What I want to do is find all other nodes that are lets say in a distance of d=.3 from that node, and do this for all nodes in the list.

What is a good vectorized way of doing this without having a double for loop?

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Answer 1

Image Analyst 2018-3-9

1
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If you have the Statistics and Machine Learning Toolbox, you can simply use pdist2() to find distances between all possible pairs of x,y locations:

% Set up:
x = randn(10,1);
y = randn(10,1);
xy = [x, y];
% Find distances between every possible pair of points:
distances = pdist2(xy, xy)
% Find distances less than 0.3
closeDistances = distances < 0.3 & distances > 0
% Get indexes of those close distances.
[rows, columns] = find(closeDistances)
% Done!  Now, for info, print out those nodes that are close
for k = 1 : length(rows)
  fprintf('Node %d and %d are close, with a distance between them of %.3f.\n',...
    rows(k), columns(k), distances(rows(k), columns(k)));
end

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Answer 2

David Fletcher 2018-3-8

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https://ww2.mathworks.cn/matlabcentral/answers/387118-find-neighboring-nodes-in-a-list-of-node-positions#answer_309099

在 MATLAB Online 中打开

Something like this:

    x = randn(10,1);
    y = randn(10,1);
    %set desired distance
    maxDistance=1.6;
    %set node of interest
    node=4;
    pos=[x y];
    nodeCoords=pos(node,:);
    %Calculate distance from specified node (euclidean)
    distFromNode=sqrt((pos(:,1)-nodeCoords(1,1)).^2+(pos(:,2)-nodeCoords(1,2)).^2);
    %Create index to points within specified maxDistance
    ind=distFromNode<=maxDistance;
    %List of node indexes within specified distance
    indexes=1:length(x);
    isWithin_Index=indexes(ind)
    %List of node coords within specified distance
    isWithin_Position=pos(ind,:)