Hi there, I was wondering what is the correct way to obtain a list of particles that lie inside each halo in a catalog. I think I can figure out how to brute force this but I was wondering if there was a YT way to do it. In the end I would like particle positions (x,y,z) for particles grouped by which halo they are in. <disclaimer> I am not an astrophysicist and did not stay in a holiday inn express last night. I don’t even know what a halo is really for. I just need to get disjoint sets of particles that are grouped together for some work I am doing with tessellation. </disclaimer> I was thinking halos calculate a position and center for clumps of particles. I would like separate lists of particle positions for each of those clumps. So far I can generate the halos (cut and paste from the docs). I just don’t know the next step. I am working with the enzo_cosmology_plus dataset as an example. Thanks, Dave Semeraro Visualization Group Texas Advanced Computing Center University of Texas Austin