MATLAB: Listing/enumerating numbers

indexingmatrix manipulation

I have the following matrix, named interact:
interact = [1 2;
            1 3; 
            2 1;
            2 3;
            3 1;
            3 4; 
            4 1]
This matrix means that 1 and 2 interact, 1 and 3 interact, and so on. (just a matrix full of indices.)
Now I want to perform this operation/task.
All that 1 interacts will be added and stored in a matrix. Meaning the interaction between 1 and 2 + interaction between 1 and 3 = interaction of 1.
Similarly, separate matrices for interaction of 2, 3, 4, etc.
How do I do this in matlab?

Best Answer

 for val=1:4
   iv{val} = interact(ismember(interact(:,1), val), 2); 
 end
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