Delete Negative Duplicates from Array

I have a 3-by-n array of points representing the vertices of a polyhedron. I need to identify all the axes that pass through the origin and a vertex, so I need to identify and remove all the points x where -x also exists in the array. I can manage this by iterating through every point and finding negatives, but it feels like there should exist a sneaky way to use the unique function to do the same thing but better.

Thanks in advance!

Answer 1

[Matt J]

X=randi(9,3,4); X=[X,-X(:,1:2)]

X = 3x6

5 8 7 6 -5 -8 4 8 9 3 -4 -8 2 5 4 1 -2 -5

map=triu(squeeze(~any(X+reshape(X,3,1,[]),1)));

[I,J]=find(map);

X(:,[I;J])=[]

X = 3x2

7 6 9 3 4 1

[Sebastian]

That's pretty impressive, but unfortunately I want to only get rid of 1 of the pair of opposite vectors, not both. For instance, in your example, I'd want it to only remove the last two columns (or just the first two). Sorry if that wasn't clear.

[Matt J]

X(:,I)=[];

Answer 2

[Catalytic]

X=rand(3,4); X=[X,-X(:,1)]

X = 3x5

0.2765 0.5016 0.7075 0.8914 -0.2765 0.8997 0.8842 0.9797 0.0281 -0.8997 0.7290 0.1868 0.9017 0.4237 -0.7290

[~,~,G]=unique([X,-X]','rows');;

[N,~,bin]=histcounts(G,1:max(G)+1);
bin=bin(1:end/2);

X(:,N(bin)>1)=[]

X = 3x3

0.5016 0.7075 0.8914 0.8842 0.9797 0.0281 0.1868 0.9017 0.4237