[yt-users] Particle Positions

Hi everyone, I'm trying to find the initial (DD0000) locations of a collection particles that form a halo at a later time. I have a list of particle IDs from that halo that I want to find the x, y, and z positions for, but I can't seem to figure out how to do for just these particles and not all the particles in the simulation. Does anyone have a suggestion on how to do this? I've been trying to use pf.h.all_data() but am stuck on getting it to only return data for this certain list of particles. Thanks, Brian