class_docstr: Create a Dataset for HuBERT model training and fine-tuning.
  
  Args:
      exp_dir (str or Path): The root directory of the ``.tsv`` file list.
      dataset (str): The dataset for training. Options: [``librispeech``, ``librilight``].
      subset (str): The subset of the dataset. Options: [``train``, ``valid``].
code: def __len__(self):
      return len(self.f_list)
  
imports: import math
  from pathlib import Path
  from typing import Dict, Iterator, List, Optional, Tuple, Union
  import numpy
  import torch
  import torch.distributed
  import torchaudio
  from torch import Tensor
  from torch.utils.data import BatchSampler, Dataset, DistributedSampler
  from ..lightning_modules import Batch
label_desc: Use image node_id 2 for calling the HuBERTDataSet obj's underlying member method code with example usage: obj.__len__() and returns: len