code: def _weighted_var(X, W, ddof):
      average = np.average(X, weights=W)
      return (
          np.average((X - average) ** 2, weights=W)
          * len(X)
          / (len(X) - ddof)
      )
  
file_path: river/river/stats/test_parallel.py
imports: from __future__ import annotations
  import copy
  import math
  import random
  import numpy
  import pytest
  from river import stats
label_desc: Use image node_id 2 for calling a global function with example usage: _weighted_var(X, W, ddof) and returns: unknown