docstr: add in a Data object the source elem, the target elem.
docstr_tok: ["add","in","a","Data","object","the","source","elem",",","the","target","elem","."]
code: def make_pair(cls, data_source, data_target):
      """
      add in a Data object the source elem, the target elem.
      """
      # add concatenation of the point cloud
      batch = cls()
      for key in data_source.keys:
          batch[key] = data_source[key]
      for key_target in data_target.keys:
          batch[key_target + "_target"] = data_target[key_target]
      if batch.x is None:
          batch["x_target"] = None
      return batch.contiguous()
  
imports: import torch
  from typing import List, Optional
  from torch_geometric.data import Data
  from torch_geometric.data import Batch
  from torch_points3d.datasets.multiscale_data import MultiScaleBatch, MultiScaleData
  import re
label_desc: Use image node_id 2 for calling the Pair obj's underlying member method code with example usage: obj.make_pair(cls, data_source, data_target) and returns: batch