def merge_constituents(self, constituent_list):
"""
returns the combination of the constituents lists
@param constituent_list list of JetConstituent objects, e.g. [jet1.constituents, jet2.constituents]
"""
ret = JetConstituents()
for elem in constituent_list:
for group in elem.values():
for ptc in group:
ret.append(ptc)
ret.sort()
return ret
