Finding Duplicate rows?

I want to find duplicate rows in my Nx2 matrix regardless of order. For instance if I were to have a matrix A

[ 1 2;

2 3;

2 1;

3 5;

4 6]

I would like to be told for instance that rows 1 and 3 are the same. Is there a quick and easy way to do this?

Thank you.

Answer 1

[madhan ravi]

Try this:

AA =sort(A,2);
U = unique(AA,'rows');
R = cell(size(AA,1),1);
for k = 1:size(U,1)
     R{k}=find(ismember(AA ,U(k,:), 'rows'));
end
Rows=R(cell2mat(cellfun(@(x)numel(x)>=2,R,'un',0)));
celldisp(Rows)

[Billy Herdman]

Works perfectly, thanks!

Answer 2

[Stephen23]

Simpler using hist (or its more recent equivalents):

>> A = [1,2;2,3;2,1;3,5;4,6;5,3] % I added an extra row
A =
   1   2
   2   3
   2   1
   3   5
   4   6
   5   3
>> [U,~,X] = unique(sort(A,2),'rows');
>> [N,E] = hist(X,1:max(X));
>> C = arrayfun(@(x)find(X==x),E(N>1),'uni',0);
>> C{:}
ans =
   1
   3
ans =
   4
   6

[Pedro Guevara]

Hi. I have one. I also need something similar to the author of the Post, however I require that each row be exactly the same (not inverted as requested by the author), that is:

A = [1,2; % This row (1) is exactly the same as (3)
    2,3;
    1,2;  % This row (3) is exactly the same as (1)
    3,5;  % This row (4) is exactly the same as (6)
    4,6;
    3,5]  % This row (6) is exactly the same as (4)

What would I have to modify in your code to make it do what I need? Thanks.

[Stephen23]

"What would I have to modify in your code to make it do what I need?"

Remove the sort function.