# Square matrix with relationships among equal rows.

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GEORGIOS BEKAS on 26 Oct 2017
Commented: Cedric Wannaz on 27 Oct 2017
I have a matrix with the following form:
A = [ 9 9 9; 5 6 5; 9 9 9; 4 4 2; 5 6 5; 5 6 5; 4 4 4; 9 9 9]
If a particular row is equal to another, I am searching for a square matrix that contains ones, when a particular row is equal to another. Therefore if row 3 is equal to row 1, I want the elements B(1,3) and B(3,1) of a new matrix B, to be equal to 1.

Andrei Bobrov on 26 Oct 2017
B = ~squareform(pdist(A));
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Andrei Bobrov on 27 Oct 2017
Thank you, Jos!

Jos (10584) on 26 Oct 2017
Edited: Jos (10584) on 26 Oct 2017
Use ismember to loop through the rows of A, and work backwards to induce automatic pre-allocation. Note that the diagonal contains 1s as well.
A = [ 9 9 9; 5 6 5; 9 9 9; 4 4 2; 5 6 5; 5 6 5; 4 4 4; 9 9 9];
B = [] ;
for k=size(A,1):-1:1
B(ismember(A,A(k,:),'rows'),k) = 1 ;
end

Cedric Wannaz on 26 Oct 2017
Edited: Cedric Wannaz on 26 Oct 2017
B = all(permute(A, [1,3,2]) == permute(A, [3,1,2]), 3) ;
and if you have a version of MATLAB < R2016b:
B = all(bsxfun(@eq, permute(A, [1,3,2]), permute(A, [3,1,2])), 3) ;
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Cedric Wannaz on 27 Oct 2017
Thank you Andrei :)