MATLAB: Clustering nearest 5 elements of a data

clustering

I have 36 points I need to find the nearest 5 elements of each point and cluster it in a group. Then there is a total of 36 clusters will get. The points are in the 'core' and I need to find the nearest elements from the 'data'. How can I do that? Please help me.

clc;
clear;
data=xlsread('Pimaxl.xlsx');
Si=size(data);
asc=sort(data);
num = numel(data);
diff=unique(asc);
core1=maxk(diff,12);
core2=mink(diff,12);
n = numel(diff(:));
midpoint = ceil(n/2);
core3 = diff(midpoint-5:midpoint+6);
cor=[core1 core2];
core=[cor core3];

Best Answer

You could do the following which is to find the 5 minimum absolute differences for each element in core.

[~,idx] = mink(abs(data(:)-core(:).'),5,1);
clusters = data(idx)

Here, the input array to mink is 6912 by 36 where each row corresponds to an element in data and each column corresponds to an element in core and contains every possible absolute difference. The mink function returns an index that you can then sub directly back into data to get your clusters. Clusters is 5 by 36 with each column corresponding to the 36 values in core.

Related Solutions

MATLAB: Core points of clusters

As discussed here, https://stackoverflow.com/questions/52364959/how-to-find-center-points-of-dbscan-clusrering-in-sklearn and here https://www.quora.com/Is-there-anything-equivalent-to-a-centroid-in-DBSCAN, dbscan does not have a center of the cluster. However, it does generate core points. You can get the core points by modifying the line in your code

core = data(corepts, :);

It will give you all rows conntaining core points. Similarly you can get the cluster number of these core points

corr_idx = idx(corepts, :);

As an example, try this

data=xlsread('glass.xlsx');
minpts=6;
epsilon=4;
[idx, corepts] = dbscan(data,epsilon,minpts);
fig1 = figure();
gscatter(data(:,1),data(:,2),idx);
fig2 = figure();
core=data(corepts, :);
corr_idx = idx(corepts, :);
gscatter(core(:,1),core(:,2),corr_idx);

MATLAB: Modify function to take input argument of marker

I don't recommend editing the source code because 1) you'll have to repeate those edits every time the file is updated and 2) it's a lot more work than the first proposal below.

Proposal 1: change the marker type after plotting

Instead, just identify all of the points marked by '.' and replace the marker type.

PlotClusters(Data,IDX,Centers,Colors);         % run the code
axh = gca;                                     % get the axis handle
h = findobj(axh, 'Marker', '.');               % find all objects that have marker '.'
set(h, 'Marker', 'x')                          % change the marker type

Proposal 2: change the function

If you must edit the source code to specify the marker type, you'll need to make these changes:

% 1) Replace the first line
% function []=PlotClusters(Data,IDX,Centers,Colors)
  function []=PlotClusters(Data,IDX,Centers,Colors,Marker)
%2) Replace this line
% plot(Data(IDX == i,1),Data(IDX == i,2),'.','Color',Colors(i,:))
  plot(Data(IDX == i,1),Data(IDX == i,2),Marker,'Color',Colors(i,:))
  
%3) Replace this line
% plot3(Data(IDX == i,1),Data(IDX == i,2),Data(IDX == i,3),'.','Color',Colors(i,:)) 
  plot3(Data(IDX == i,1),Data(IDX == i,2),Data(IDX == i,3),Marker,'Color',Colors(i,:)) 
  
%4) Replace this line
% case 4 %All data is given just need to check consistency    
  case {4,5} %All data is given just need to check consistency  
      
%5 After the switch add these lines
if nargin < 5 || isempty(Marker)
    Marker = '.'; 
end

* Not tested!

** I recommend the first proposal!

Best Answer

Related Solutions

MATLAB: Core points of clusters

MATLAB: Modify function to take input argument of marker

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