MATLAB: Form a matrix with variable number of columns (with fixed row numbers)

variable number of columns

I'm clustering a 70,000×3 data matrix(say X is data and K is no. of clusters). For that I want to store the index value (positions) of data points belonging to each cluster(required for further calculations and work) . As per the problem, it would be like Y[c, j] (c = cluster number, j = index vslue of data point ). But, the clusters formed isn't equally distributed. The number of data points belonging to different clusters will be different. Is there a way to form such matrix with variable number of columns and fixed number of rows? If not, please suggest the another way.

Thanks in advance !

Best Answer

Just store the cluster number for each point. If you need to know which points belong to one particular cluster then use logical masks idx == cluster_number or find(idx == cluster_number). If you do that a lot, then calculate it once and store in cell arrays.

If it is for some reason particularly important to store everything in a single numeric array, then zero pad or nan pad the shorter rows.

Related Solutions

MATLAB: How i can solve this problem? Pleas!

Your ‘T’ matrix must become a cell array. See my sample of ‘T’ for an example.

Once you do that, I would do something like this:

Y = [12.004
    13.1573 
    11.1665  
    11.8082    
    12.2129   
    12.8075   
    12.4167  
    11.5708   
    12.5798    
    13.7489];
T={'cluster2'; 'cluster1'; 'cluster3'; 'cluster9'; 'cluster0'; 'cluster7'; 'cluster4'}; % Sample Of Cell Array
[UnqClust,~,idx] = unique(T);                                                           % Unique Values & Locations
Out = Y(idx);                                                                           % Mapped Output
for k1 = 1:length(idx)
    fprintf(1, '\t%s\t%.4f\n', T{k1}, Out(k1))              % Demonstration Output (Delete Loop)
end
  cluster2  11.1665
  cluster1  13.1573
  cluster3  11.8082
  cluster9  12.4167
  cluster0  12.0040
  cluster7  12.8075
  cluster4  12.2129

MATLAB: I want solution for this problem

This code might do what you are looking for

ix = sscanf( T(:,end), '%1d' );
Y  = cat( 1, Y, rand );     % add one element to get 10
R  = Y(ix+1);

inspect the result

>> R(1:6)'
ans =
   11.1665   11.1665   11.1665   11.5740   11.5740   11.5740

where

T=['cluster2'
'cluster2'
'cluster2'
'cluster7'
'cluster7'
'etc ....'];

Best Answer

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MATLAB: How i can solve this problem? Pleas!

MATLAB: I want solution for this problem

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