code: def _sample_mask(idx, l):
      """Create mask."""
      mask = np.zeros(l)
      mask[idx] = 1
      return mask
  
imports: from __future__ import absolute_import
  import os, sys
  import pickle
  import warnings
  import networkx
  import numpy
  import scipy.sparse
  from ..None import backend, batch, convert
  from ..convert import from_networkx, graph, to_networkx
  from ..transforms import reorder_graph
  from .dgl_dataset import DGLBuiltinDataset
  from .utils import _get_dgl_url, deprecate_function, deprecate_property, generate_mask_tensor, load_graphs, load_info, makedirs, save_graphs, save_info
label_desc: Use image node_id 4 for calling a global function with example usage: _sample_mask(idx, l) and returns: mask