How can I remove certain vertical edges, as seen here in the image?
Chris's answer is flawless, and it works beautifully.
However, if you want to select the edges based on a direction vector (and maybe even define a certain tolerance value), then this solution might be almost a little better. ...at least you even save a whole node ;-)
PS: With Epsilon you define the tolerance, and with the vector $B$ the direction.
You can also use this technique to filter any other edge. For example, you can select all vertical edges.
Or you can simply reverse the selection with the
Boolean Math node, which will also remove all non-vertical edges: