MATLAB: Segregate various elements of a matrix into separate groups based on their close proximity

grouping elements in a matrix into separate groupsStatistics and Machine Learning Toolbox

Hello, I have a 2D matrix that I have created from filtering a contour map of an image and I created a regional maxima of the final image as shown in the attached photo. now the matrix contains only ones and zeros in a random order. I need now to group all the points with "ones" that are in close proximity into a single group and know the raw and column matrix indexes of the first element of each group. this to be applied to all groups. I do not want to do this manually, as I want to apply this algortihm to thousands of matrices that have their regional maxima distributed randomly. I need to know if there is a certain function/exchange file in matlab that can manage to segregate these groups. please find attached photo for more explanation of what I need. Thanks in advance.

Best Answer

Do you know how many groups there will be? If so, just get the x and y coordinates of each point using find(), then pass them into kmeans().

If you don't know then you could use some other clustering technique, like dbscan.

Or you could use pdist2() and cluster that by thresholding. It would be simple but it would probably require that the groups be well separated (unlike dbscan).

There are other unsupervised clustering methods that you can use. Take a deeper dive here: https://www.mathworks.com/help/stats/cluster-analysis.html

Related Solutions

MATLAB: Putting similar numbers into groups within an array

If you have the Statistics and Machine Learning Toolbox (for pdist2) and the Image Processing Toolbox (for bwlabel), you can do this:

m = [...
7340.1
7340.3
7340.6
7349.0
7349.4
7358.0
7358.1
7358.2
7358.7]
% % New groups would look like follows:
% % Group 1
% 7340.1
% 7340.3
% 7340.6
% % Group 2
% 7349.0
% 7349.4
% % Group 3
% 7358.0
% 7358.1
% 7358.2
% 7358.7]
% First sort m so that close by ones has adjacent indexes.
m = sort(m, 'ascend')
% Get distance of every element to every other element.
distances = pdist2(m, m)
% Find out which pairs are within 2 of each other.
within2 = distances > 0 & distances < 2
% Erase upper triangle to get rid of redundancy
numElements = numel(m);
t = logical(triu(ones(numElements, numElements), 0))
within2(t) = 0
% Label each group with an ID number.
[labeledGroups, numGroups] = bwlabel(within2)
% Put each group into a cell array
for k = 1 : numGroups
  [rows, columns] = find(labeledGroups == k);
  indexes = unique([rows, columns]);
  groups{k} = m(indexes);
end
celldisp(groups); % Display the results in the command window.

It gives you your desired result. Should work for other arrays also, though I didn't test it with any others.

MATLAB: Segregate data

out = reshape(P,numel(P)/2,[])'

out = mat2cell(P,1,numel(P)/2*[1 1])

t = P < 100;
out = {P(t) P(~t)}

Best Answer

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MATLAB: Putting similar numbers into groups within an array

MATLAB: Segregate data

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