class_docstr: Represent records of user-item with features.
  
  Each record should contain the following fields:
  user_id: Positive int.
  item_id: Positive int.
  sample: Sample which consists of feature(s) and label(s).
class_docstr_tok: ["Represent","records","of","user-item","with","features",".","Each","record","should","contain","the","following","fields",":","user_id",":","Positive","int",".","item_id",":","Positive","int",".","sample",":","Sample","which","consists","of","feature","(","s",")","and","label","(","s",")","."]
code: def __reduce__(self):
      return UserItemFeature, (self.user_id, self.item_id, self.sample)
  
imports: import sys
  from pyspark import RDD
  from zoo.models.common import *
  from zoo.common.utils import callZooFunc
label_desc: Use image node_id 2 for calling the UserItemFeature obj's underlying member method code with example usage: obj.__reduce__() and returns: UserItemFeature,  self,  self,  self