class_docstr: Variance Ratio split criterion.
  
  Parameters
  ----------
  min_samples_split
      The minimum number of samples per post split dist element.
code: def merit_of_split(self, pre_split_dist, post_split_dist):
      vr = 0
      n = pre_split_dist.mean.n
  
      count = 0
      for i in range(len(post_split_dist)):
          n_i = post_split_dist[i].mean.n
          if n_i >= self.min_samples_split:
              count += 1
      if count == len(post_split_dist):
          vr = 1
          var = self.compute_var(pre_split_dist)
          for i in range(len(post_split_dist)):
              n_i = post_split_dist[i].mean.n
              vr -= (n_i / n) * (
                  self.compute_var(post_split_dist[i]) / var
              )
      return vr
  
file_path: river/river/tree/split_criterion/variance_ratio_split_criterion.py
imports: from __future__ import annotations
  from .base import SplitCriterion
label_desc: Use image node_id 2 for calling the VarianceRatioSplitCriterion obj's underlying member method code with example usage: obj.merit_of_split(pre_split_dist, post_split_dist) and returns: vr