Find neighboring nodes in a list of node positions

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?

Answer 1

[Image Analyst]

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

Answer 2

[David Fletcher]

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,:)

Though you may want to modify it so that the node doesn't report that it is within maxDistance of itself