Square matrix with relationships among equal rows.

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.

Answer 1

[Andrei Bobrov]

B = ~squareform(pdist(A));

[Jos (10584)]

nice one, Andrei! +1

[Andrei Bobrov]

Thank you, Jos!

Answer 2

[Jos (10584)]

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

Answer 3

[Cedric Wannaz]

 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) ;

[Andrei Bobrov]

+1. My favorite "plows"!

[Cedric Wannaz]

Thank you Andrei :)