code: def __len__(self):
      return self.samples_mapping.shape[0]
  
file_path: megatron-lm/megatron/data/t5_dataset.py
imports: import collections
  import numpy
  import torch
  from megatron import get_tokenizer
  from megatron.data.dataset_utils import create_masked_lm_predictions, get_samples_mapping
label_desc: Use image node_id 2 for calling the T5Dataset obj's underlying member method code with example usage: obj.__len__() and returns: self