class_docstr: Head of GNN, node prediction
class_docstr_tok: ["Head","of","GNN",",","node","prediction"]
code: def _apply_index(self, batch):
      mask = "{}_mask".format(batch.split)
      return batch.x[batch[mask]], batch.y[batch[mask]]
  
imports: import torch
  import torch.nn
  import graphgym.register
  from graphgym.config import cfg
  from graphgym.models.layer_pyg import MLP
  from graphgym.models.pooling import pooling_dict
label_desc: Use image node_id 2 for calling the GNNNodeHead obj's underlying member method code with example usage: obj._apply_index(batch) and returns: batch,  batch