code: def _mean_of_y(self, y):
      value = np.mean(y, axis=0)
      return value if len(value) > 1 else value[0]
  
imports: from __future__ import division, print_function
  import numpy
  from mlfromscratch.utils import divide_on_feature, train_test_split, standardize, mean_squared_error
  from mlfromscratch.utils import calculate_entropy, accuracy_score, calculate_variance
label_desc: Use image node_id 2 for calling the RegressionTree obj's underlying member method code with example usage: obj._mean_of_y(y) and returns: unknown