Remove specific points from selection? (curve endpoints/geometry nodes)

[grant.r.brown]

Hello.

How do I remove specific points from a selection - in this case a set of curves?

e.g. in this node tree I have a bunch of curve line instances. I use the index with a modulo to select points along these curves and apply a random offset. But how would I stop this offset being applied to the base of each curve? I want the startpoint of each curve to align to whatever the base mesh is (so I suppose I need to capture normals somewhere and then aling to Euler?).

So how do I phrase this selection in nodes? I tried using curve endpoint selection with a boolean math (tried both not and subtract) but it seemed to give results I didn’t understand.

I seem to often be in this circumstance where I want to apply something to “a selection without something else” and I rarely manage to figure it out.

Slime Mold GN setup.blend (1.2 MB)

[Hadriscus]

Hi, yes curve endpoints should work. If you pipe it into a “not” boolean math node, you’ll get a selection that contains every point except the endpoints.

To clarify, you can use the boolean math node to combine selections this way :
NOT will invert the input selection
OR will add two different input selections
AND will select only the elements that are selected in both input selections

[grant.r.brown]

Aha!

Seems I was overcomplicating this by trying to keep the index + modulo and then the endpoint selection - I keep trying to approach this like shaders with a mix node, which I think isn’t the right way for this sort of thing.

Thanks!

[edit] This is the node setup that does what I want as in original post: