code: def _get_ori_dataset_idx(self, idx):
      dataset_idx = bisect.bisect_right(self.cumulative_sizes, idx)
      sample_idx = (
          idx
          if dataset_idx == 0
          else idx - self.cumulative_sizes[dataset_idx - 1]
      )
      return dataset_idx, sample_idx
  
imports: import bisect
  from unittest import TestCase
  from unittest.mock import patch
  import numpy
  from torch.utils.data import ConcatDataset, Dataset
  from mmdet.datasets.samplers import GroupMultiSourceSampler, MultiSourceSampler
label_desc: Use image node_id 1 for calling the DummyConcatDataset obj's underlying member method code with example usage: obj._get_ori_dataset_idx(idx) and returns: dataset_idx,  sample_idx