class_docstr: A struct for fully describing a fixed-size block of data as used in REALM
  
  :param start_idx: for first sentence of the block
  :param end_idx: for last sentence of the block (may be partially truncated in sample construction)
  :param doc_idx: the index of the document from which the block comes in the original indexed dataset
  :param block_idx: a unique integer identifier given to every block.
code: def as_array(self):
      return np.array(
          [self.start_idx, self.end_idx, self.doc_idx, self.block_idx]
      ).astype(np.int64)
  
imports: import os
  import time
  import numpy
  import torch
  from megatron import print_rank_0
  from megatron.core import mpu, tensor_parallel
  from megatron.data.dataset_utils import create_masked_lm_predictions, pad_and_convert_to_numpy
  from megatron import get_args, get_tokenizer, print_rank_0
label_desc: Use image node_id 2 for calling the BlockSampleData obj's underlying member method code with example usage: obj.as_array() and returns: np