code: def prepare_pos_tagging_data(self):
      index = "index"
      ds = DataSet({index: list(range(N_SAMPLES))})
      ds.apply_field(
          lambda x: self.gen_var_seq(MAX_LEN, VOCAB_SIZE),
          field_name=index,
          new_field_name="words",
      )
      ds.apply_field(
          lambda x: self.gen_seq(len(x), NUM_CLS),
          field_name="words",
          new_field_name="target",
      )
      ds.apply_field(len, "words", "seq_len")
      dl = TorchDataLoader(ds, batch_size=BATCH_SIZE)
      return dl
  
file_path: fastNLP/tests/models/torch/model_runner.py
imports: from fastNLP.envs.imports import _NEED_IMPORT_TORCH
  from fastNLP import Trainer, Evaluator, DataSet, Callback
  from fastNLP import Accuracy
  from random import randrange
  from fastNLP import TorchDataLoader
label_desc: Use image node_id 4 for calling the ModelRunner obj's underlying member method code with example usage: obj.prepare_pos_tagging_data() and returns: dl