Hi all, sorry, I have a pretty dumb question. I have a non-cosmological simulation with only 1 particle. I can get the particle_mass field, but yt throws the following error when I try to grab particle_index: --------------------------------------------------------------------------------------------------------------------------------- In [1]: pf = load('CE0001') yt : [INFO ] 2013-04-24 00:32:02,190 Parameters: current_time = 0.00149998503444 yt : [INFO ] 2013-04-24 00:32:02,190 Parameters: domain_dimensions = [32 32 32] yt : [INFO ] 2013-04-24 00:32:02,190 Parameters: domain_left_edge = [ 0. 0. 0.] yt : [INFO ] 2013-04-24 00:32:02,190 Parameters: domain_right_edge = [ 1. 1. 1.] yt : [INFO ] 2013-04-24 00:32:02,191 Parameters: cosmological_simulation = 0.0 In [2]: region = pf.h.region([0.5, 0.5, 0.5], [0.0, 0.0, 0.0], [1.0, 1.0, 1.0]) yt : [INFO ] 2013-04-24 00:32:05,802 Getting the binary hierarchy yt : [INFO ] 2013-04-24 00:32:05,805 Finished with binary hierarchy reading In [3]: region['particle_mass'] yt : [INFO ] 2013-04-24 00:32:12,685 Getting particle_mass using ParticleIO Out[3]: array([ 6585896.1408]) In [4]: region['particle_index'] --------------------------------------------------------------------------- KeyError Traceback (most recent call last) /Users/jcpassy/Work/yt-x86_64/src/yt-hg/scripts/iyt in <module>() ----> 1 region['particle_index'] /Users/jcpassy/Work/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.pyc in __getitem__(self, key) 328 if key not in self.fields: 329 self.fields.append(key) --> 330 self.get_data(key) 331 return self.field_data[key] 332 /Users/jcpassy/Work/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.pyc in get_data(self, fields, in_grids, force_particle_read) 2614 pass 2615 if field not in self.hierarchy.field_list and not in_grids: -> 2616 if self._generate_field(field): 2617 continue # True means we already assigned it 2618 mylog.info("Getting field %s from %s", field, len(self._grids)) /Users/jcpassy/Work/yt-x86_64/src/yt-hg/yt/data_objects/data_containers.pyc in _generate_field(self, field) 361 return True 362 else: # Can't find the field, try as it might --> 363 raise KeyError(field) 364 365 def _generate_field_in_grids(self, field, num_ghost_zones=0): KeyError: 'particle_index' --------------------------------------------------------------------------------------------------------------------------------- However, the field is there: --------------------------------------------------------------------------------------------------------------------------------- [ 0:30:13] Obiwan:$ h5ls CE0001.cpu0000/Grid00000004 Dark_Matter_Density Dataset {52, 52, 52} Density Dataset {52, 52, 52} TotalEnergy Dataset {52, 52, 52} particle_index Dataset {1} particle_mass Dataset {1} particle_position_x Dataset {1} particle_position_y Dataset {1} particle_position_z Dataset {1} particle_type Dataset {1} particle_velocity_x Dataset {1} particle_velocity_y Dataset {1} particle_velocity_z Dataset {1} x-velocity Dataset {52, 52, 52} y-velocity Dataset {52, 52, 52} z-velocity Dataset {52, 52, 52} [ 0:30:13] Obiwan:$ h5ls -d CE0001.cpu0000/Grid00000004/particle_index particle_index Dataset {1} Data: (0) 0 --------------------------------------------------------------------------------------------------------------------------------- Am I missing something obvious? Thanks a lot for you help, JC