code: def graph_build_zero_filling(X, edge_index, node_mask: torch.Tensor):
      """subgraph building through masking the unselected nodes with zero features"""
      ret_x = X * node_mask.unsqueeze(1)
      return ret_x, edge_index
  
imports: import torch
  import numpy
  from torch_geometric.data import Data
  from dig.xgraph.dataset import MarginalSubgraphDataset
label_desc: Use image node_id 1 for calling a global function with example usage: graph_build_zero_filling(X, edge_index, node_mask) and returns: ret_x,  edge_index