def _kill_subtree(self, node: AnyTimeSplitNode):
""" Kill subtree that starts from node.
Parameters
----------
node: AnyTimeActiveLearningNode
The node to reevaluate.
Returns
-------
AnyTimeActiveLearningNode
The new leaf.
"""
leaf = self._new_learning_node()
leaf.set_observed_class_distribution(node.get_observed_class_distribution())
leaf.set_attribute_observers(node.get_attribute_observers())
return leaf
def _reevaluate_best_split(self, node: AnyTimeSplitNode, parent,
branch_index):
""" Reevaluate the best split for a node.
If the samples seen so far are not from the same class then:
1. Find split candidates and select the best one.
2. Compute the Hoeffding bound.
3. If the don't split candidate is higher than the top split candidate:
3.1 Kill subtree and replace it with a leaf.
3.2 Update the tree.
3.3 Update tree's metrics
4. If the difference between the top split candidate and the current split is larger than
the Hoeffding bound:
4.1 Create a new split node.
4.2 Update the tree.
4.3 Update tree's metrics
5. If the top split candidate is the current split but with different split test:
5.1 Update the split test of the current split.
Parameters
----------
node: AnyTimeSplitNode
The node to reevaluate.
parent: AnyTimeSplitNode
The node's parent.
branch_index: int
Parent node's branch index.
Returns
-------
boolean
flag to stop moving in depth.
"""
stop_flag = False
if not node.observed_class_distribution_is_pure():
if self._split_criterion == GINI_SPLIT:
split_criterion = GiniSplitCriterion()
elif self._split_criterion == INFO_GAIN_SPLIT:
split_criterion = InfoGainSplitCriterion()
else:
split_criterion = InfoGainSplitCriterion()
best_split_suggestions = node.get_best_split_suggestions(
split_criterion, self)
if len(best_split_suggestions) > 0:
# Compute Gini (or Information Gain) for each attribute (except the null one)
best_split_suggestions.sort(key=attrgetter('merit'))
# x_best is the attribute with the highest G_int
x_best = best_split_suggestions[-1]
id_best = x_best.split_test.get_atts_test_depends_on()[0]
# x_current is the current attribute used in this SplitNode
id_current = node.get_split_test().get_atts_test_depends_on(
)[0]
x_current = node.find_attribute(id_current,
best_split_suggestions)
# Get x_null
x_null = node.get_null_split(split_criterion)
# Force x_null merit to get 0 instead of -infinity
if x_null.merit == -np.inf:
x_null.merit = 0.0
# Compute Hoeffding bound
hoeffding_bound = self.compute_hoeffding_bound(
split_criterion.get_range_of_merit(
node.get_observed_class_distribution()),
self.split_confidence, node.get_weight_seen())
if x_null.merit - x_best.merit > hoeffding_bound:
# Kill subtree & replace the AnyTimeSplitNode by AnyTimeActiveLearningNode
best_split = self._kill_subtree(node)
# update EFDT
if parent is None:
# Root case : replace the root node by a new split node
self._tree_root = best_split
else:
parent.set_child(branch_index, best_split)
deleted_node_cnt = node.count_nodes()
self._active_leaf_node_cnt += 1
self._active_leaf_node_cnt -= deleted_node_cnt[1]
self._decision_node_cnt -= deleted_node_cnt[0]
stop_flag = True
# Manage memory
self.enforce_tracker_limit()
elif (x_best.merit - x_current.merit > hoeffding_bound
or hoeffding_bound < self.tie_threshold) and (
id_current != id_best):
# Create a new branch
new_split = self.new_split_node(
x_best.split_test,
node.get_observed_class_distribution(),
node.get_attribute_observers())
# Update weights in new_split
new_split.update_weight_seen_at_last_split_reevaluation()
# Update EFDT
for i in range(x_best.num_splits()):
new_child = self._new_learning_node(
x_best.resulting_class_distribution_from_split(i))
new_split.set_child(i, new_child)
deleted_node_cnt = node.count_nodes()
self._active_leaf_node_cnt -= deleted_node_cnt[1]
self._decision_node_cnt -= deleted_node_cnt[0]
self._decision_node_cnt += 1
self._active_leaf_node_cnt += x_best.num_splits()
if parent is None:
# Root case : replace the root node by a new split node
self._tree_root = new_split
else:
parent.set_child(branch_index, new_split)
stop_flag = True
# Manage memory
self.enforce_tracker_limit()
elif (x_best.merit - x_current.merit > hoeffding_bound or
hoeffding_bound < self.tie_threshold) and (id_current
== id_best):
node._split_test = x_best.split_test
return stop_flag