extracting columns with comparison

Hi

Given I would have (as a toy example) a matrix A like:

A = [ 5 7 -5; 3 8 3; 2 9 2]

I would want to extract the indices of the pairs of columns which have the same y and z values but a negative x value of each other. So for the example this is true for the first and third column (the x values are 5 and -5 respectively, and the y value is 3 for both and the z value is 2 for both too). How would I do that?

Answer 1

[Andrei Bobrov]

B = A;
B(1,:) = abs(B(1,:));
[a,~,c] = unique(B.','rows');
out = [accumarray(c,(1:numel(c))',[],@(x){x})';num2cell(a',1)];