docstr: Randomly selects a known and unknown item to a particular user.
  
  :param user: User to generate pairs
  :type user: int
  
  :return: known item, unknown item
docstr_tok: ["Randomly","selects","a","known","and","unknown","item","to","a","particular","user",".",":","param","user",":","User","to","generate","pairs",":","type","user",":","int",":","return",":","known","item",",","unknown","item"]
code: def sample_pair(self, user):
      """
      Randomly selects a known and unknown item to a particular user.
  
      :param user: User to generate pairs
      :type user: int
  
      :return: known item, unknown item
  
      """
      return random.choice(
          list(self.train_set["items_seen_by_user"][user])
      ), random.choice(self.train_set["items_unobserved"][user])
  
file_path: CaseRecommender/caserec/recommenders/item_recommendation/bprmf.py
imports: import random
  import numpy
  from caserec.recommenders.item_recommendation.base_item_recommendation import BaseItemRecommendation
  from caserec.utils.extra_functions import timed
label_desc: Use image node_id 5 for calling the BprMF obj's underlying member method code with example usage: obj.sample_pair(user) and returns: random,  random