code: def __len__(self):
      length = len(self.chosen)
      return length
  
imports: import copy
  import json
  from typing import Dict, Sequence
  import torch
  from torch.utils.data import Dataset
  from tqdm import tqdm
  from transformers import AutoTokenizer
label_desc: Use image node_id 2 for calling the EasyRewardDataset obj's underlying member method code with example usage: obj.__len__() and returns: length