MATLAB: How to group scattered points that visually belong to lines

clusteringMATLAB

Hi there,

I have a set of scattered points look like this:

The data are stored in a x-vector and a y-vector and the sequence is random.

By visual, it is apparent that there are five lines from left to right and a V-shaped group of points, but how can I group the points that fall on the lines into separate arrays by code?

Thanks.

Best Answer

The data you provided was helpful. This should get you started. Check out the documentation for clusterdata() so you can tweak this if you decide to continue with this route.

The 'idx' variable below indicates the group number for each (X,Y) pair.

load('scattered points.mat')
idx = clusterdata([X',Y'],6); 
gscatter(X,Y,idx)

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MATLAB: Coloring The Dots in biPlot Chart

The biplot() function has an output that lists handles to all objects in the plot. All you need to do is isolate the handles to the scatter points by referencing the handle tags and then assign color based on the category.

If you have any questions, feel free to leave a comment.

% Your code
categories = ['F1';'F2';'F3';'F4';'F5';'F6';'F7';'F8'];
load('MAT_ALL.mat')
% figure(1)  (No need for this)
[coefforth,score,~,~,explainedVar] = pca(MaT_All(:,9:16));
load('DataGroup.mat')
clusters = DataGroup(:,20);
[coefforth,score,~,~,explainedVar] = pca(MaT_All(:,9:16));
figure()
% Store handle to biplot
h = biplot([coefforth(:,1) coefforth(:,2)],'Scores',[score(:,1) score(:,2)],'Varlabels',categories);
% Identify each handle
hID = get(h, 'tag'); 
% Isolate handles to scatter points
hPt = h(strcmp(hID,'obsmarker')); 
% Identify cluster groups
grp = findgroups(clusters);    %r2015b or later - leave comment if you need an alternative
grp(isnan(grp)) = max(grp(~isnan(grp)))+1; 
grpID = 1:max(grp); 
% assign colors and legend display name
clrMap = lines(length(unique(grp)));   % using 'lines' colormap
for i = 1:max(grp)
    set(hPt(grp==i), 'Color', clrMap(i,:), 'DisplayName', sprintf('Cluster %d', grpID(i)))
end
% add legend to identify cluster
[~, unqIdx] = unique(grp);
legend(hPt(unqIdx))

You can select a different color map (I'm using 'lines'). : https://www.mathworks.com/help/matlab/ref/colormap.html#buc3wsn-1-map 190425 094457-Figure 1.jpg

MATLAB: Cluster Head in Kmeans Clustering

x = rand(1000,1) ; y = rand(1000,1) ;    % random points 
N = 4 ;    % number of groups 
[idx,C,sumd] = kmeans([x y],N) ;  % apply kmeans 
figure
hold on
for i = 1:N
    plot(x(idx==i),y(idx==i),'.') ;
    plot(C(i,1),C(i,2),'*')
end

In the above C is the cluster head.....cluster head/ cluster centroid is nothing but the mean values of x and y of each group.

Best Answer

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MATLAB: Coloring The Dots in biPlot Chart

MATLAB: Cluster Head in Kmeans Clustering

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