How to find set of 3 in a 122x4 matrix?

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John Hunt 2017-10-13

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评论： John Hunt 2017-10-17

I have a matrix that is 122x4. These have index numbers 1-36 with two only rows containing three points that are common between them. How can I find these pairs?

A=[ 1 2 13 15;
2 15 35;
2 17 22;
2 22 36...]

(there is not a pattern throughout the matrix like there are in the first couple rows) I want some thing that can identify the pair of combos

combos = [1 2;
          3 4]

where 1,2,3,and 4 are row numbers

If I can also print out the numbers they share that would be great too combos = [1 2 1 2 15;...etc

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dpb 2017-10-17

Say what!!!??? I have no klew what the above is intending to say.

Are the three values you're trying to match those in the first three columns only or is it three out of the four in the line that are to be found?

John Hunt 2017-10-17

three out of the four need to match three out of four for the other rows

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Guillaume 2017-10-17

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编辑：Guillaume 2017-10-17

在 MATLAB Online 中打开

This is O(n^2) so is going to be slow for largish matrices. I haven't got the time to think of a cleverer algorithm:

pairs = zeros(0, 5);
for row1 = 1 : size(A, 1)
   for row2 = row1+1 : size(A, 1)
      commonnumbers = intersect(A(row1, :), A(row2, :));
      if numel(commonnumbers ) == 3
         pairs = [pairs; row1, row2, commonnumbers]; %#ok<AGROW>
         break;  %assumes that there is always only one other row that matches
      end
   end
end