Writing hepfiles from Dictionaries

# imports
import hepfile as hf

Say that we have two events in a particle physics experiment and we measured the x and y momentum for both the jets and muons for each as well as the number of particles emitted. Each event can be represented as a nested dictionary:

event1 = {
    'jet': {
        'px': [1,2,3],
        'py': [1,2,3]
     },
    'muons': {
        'px': [1,2,3],
        'py': [1,2,3]
     },
    'nParticles': 3
    }

event2 = {
    'jet': {
        'px': [3,4,6,7],
        'py': [3,4,6,7]
     },
    'muons': {
        'px': [3,4,6,7],
        'py': [3,4,6,7],
        },
    'nParticles': 4
    }

Note how these events do not have the same number of particles emitted and therefore could not be stored in a typical “homogeneous” data structure. This is where hepfile becomes useful!

To easily create a hepfile from these events we can store them in a list:

to_write_to_hepfile = [event1, event2]

Then, to write this out to a hepfile, we simply need to use the dict_tools module of hepfile.

out_filename = 'output_from_dict.hdf5'
data = hf.dict_tools.dictlike_to_hepfile(to_write_to_hepfile, out_filename)
data

{'_GROUPS_': {'_SINGLETONS_GROUP_': ['COUNTER', 'nParticles'],
  'jet': ['njet', 'px', 'py'],
  'muons': ['nmuons', 'px', 'py']},
 '_MAP_DATASETS_TO_COUNTERS_': {'_SINGLETONS_GROUP_': '_SINGLETONS_GROUP_/COUNTER',
  'jet': 'jet/njet',
  'jet/px': 'jet/njet',
  'jet/py': 'jet/njet',
  'muons': 'muons/nmuons',
  'muons/px': 'muons/nmuons',
  'muons/py': 'muons/nmuons',
  'nParticles': '_SINGLETONS_GROUP_/COUNTER'},
 '_LIST_OF_COUNTERS_': ['_SINGLETONS_GROUP_/COUNTER',
  'jet/njet',
  'muons/nmuons'],
 '_SINGLETONS_GROUP_/COUNTER': [1, 1],
 '_MAP_DATASETS_TO_DATA_TYPES_': {'_SINGLETONS_GROUP_/COUNTER': int,
  'jet/njet': int,
  'jet/px': numpy.int64,
  'jet/py': numpy.int64,
  'muons/nmuons': int,
  'muons/px': numpy.int64,
  'muons/py': numpy.int64,
  'nParticles': numpy.int64},
 '_META_': {},
 'jet/njet': [3, 4],
 'jet/px': [1, 2, 3, 3, 4, 6, 7],
 'jet/py': [1, 2, 3, 3, 4, 6, 7],
 'muons/nmuons': [3, 4],
 'muons/px': [1, 2, 3, 3, 4, 6, 7],
 'muons/py': [1, 2, 3, 3, 4, 6, 7],
 'nParticles': [3, 4]}