MATLAB: How to Group strings

groupingMATLAB

Hi Everyone,

How can I group strings based on their values?

Example: a=[1 2 3 4]; b=[0 5 3 5]; c=[9 4 7 7]; d=[9 7 3 1];

I want to make a group of the strings that have value of 3 in their 3rd column. Those will be a,b and d.

Can 1 string perticipate in more than one groups? For example Group 1 is the already mentioned one, and Group 2 would be made of the strings that have value of 9 in the 1st column. Those will be strings c and d.

Cheers, Vihar

Best Answer

Storing the data in different variables is not efficient. This would be much faster and easier to expand:

Data = [1 2 3 4; ...
        0 5 3 5; ...
        9 4 7 7; ...
        9 7 3 1];
Group{1} = find(Data(:, 3) == 3);
Group{2} = find(Data(:, 1) == 9);

And even the outputs should not be numbered, but collected in a cell array.

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MATLAB: How to compare elements of rows within cell array

for k=1:size(array1,1)
    for j=1:numel(array1{k,1})
        for i=1:size(array1,1)
            [~,idx(i,j,k)]=ismember(array1{k,1}(j),array1{i,1});
        end
        ResultantArray{k,j}=setdiff(find(idx(:,j,k)),k);
    end
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MATLAB: How to generate a specific group of numbers from nchoosek

If I have interpreted your request correctly, you can do what you ask with two calls on 'nchoosek', one to choose three numbers out of nine and the other to choose three numbers out of six, (plus some additional processing of course.) What I have understood is that you want to generate all possible ways of dividing up the numbers from 1 to 9 into three groups with three numbers in each group. The total number of these is 9!/3!/3!/3! = 1680.

 C1 = nchoosek(1:9,3);
 C1 = [C1,zeros(size(C1,1),6)];
 x = 1:9;
 for p = 1:size(C1,1)
   t = true(1,9); t(C1(p,1:3)) = false(1,3);
   C1(p,4:9) = x(t);
 end
 C2 = nchoosek(1:6,3);
 C2 = [C2,zeros(size(C2,1),3)];
 x = 1:6;
 for q = 1:size(C2,1)
   t = true(1,6); t(C2(q,1:3)) = false(1,3);
   C2(q,4:6) = x(t);
 end
 A = zeros(size(C1,1)*size(C2,1),9);
 k = 0;
 for p = 1:size(C1,1)
   x = C1(p,1:3);
   y = C1(p,4:9);
   for q = 1:size(C2,1)
     k = k + 1;
     A(k,:) = [x,y(C2(q,:))];
   end
 end

The matrix A which has nine columns will contain your desired three groups: A(:,1:3), A(:,4:6), and A(:,7:9).

Best Answer

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MATLAB: How to compare elements of rows within cell array

MATLAB: How to generate a specific group of numbers from nchoosek

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