docstr: save the mapping dict that maps node IDs to embedding indices
docstr_tok: ["save","the","mapping","dict","that","maps","node","IDs","to","embedding","indices"]
code: def save_mapping(self, map_file):
      """save the mapping dict that maps node IDs to embedding indices"""
      with open(map_file, "wb") as f:
          pickle.dump(self.node2id, f)
  
imports: import os
  import pickle
  import random
  import time
  import dgl
  import numpy
  import scipy.sparse
  import torch
  from dgl.data.utils import _get_dgl_url, download, extract_archive, get_download_dir
  from torch.utils.data import DataLoader
  from utils import shuffle_walks
label_desc: Use image node_id 3 for calling the DeepwalkDataset obj's underlying member method code with example usage: obj.save_mapping(map_file) without return types