docs: def filter_and_save(raw, symbol_ids, destination_path):
      """
      Parameters
      ----------
      raw : dict
          with key 'handwriting_datasets'
      symbol_ids : dict
          Maps LaTeX to write-math.com id
      destination_path : str
          Path where the filtered dict 'raw' will be saved
      """
      logging.info('Start filtering...')
      new_hw_ds = []
      for el in raw['handwriting_datasets']:
          if el['formula_id'] in symbol_ids:
              el['formula_id'] = symbol_ids[el['formula_id']]
              el['handwriting'].formula_id = symbol_ids[el['formula_id']]
              new_hw_ds.append(el)
      raw['handwriting_datasets'] = new_hw_ds
  
      # pickle
      logging.info('Start dumping %i recordings...', len(new_hw_ds))
      pickle.dump(raw, open(destination_path, "wb"), 2)