def _attempt_to_split(self, node, parent, branch_index):
""" Attempt to split 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 difference between the best split candidate and the don't split candidate is larger than
the Hoeffding bound:
3.1 Replace the leaf node by a split node.
3.2 Add a new leaf node on each branch of the new split node.
3.3 Update tree's metrics
Parameters
----------
node: AnyTimeActiveLearningNode
The node to reevaluate.
parent: AnyTimeSplitNode
The node's parent.
branch_index: int
Parent node's branch index.
"""
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:
# x_best is the attribute with the highest G_int
best_split_suggestions.sort(key=attrgetter('merit'))
x_best = best_split_suggestions[-1]
# 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
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_best.merit - x_null.merit > hoeffding_bound or hoeffding_bound < self.tie_threshold:
# Split
new_split = self.new_split_node(
x_best.split_test,
node.get_observed_class_distribution(),
node.get_attribute_observers())
# update weights in
new_split.update_weight_seen_at_last_split_reevaluation()
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)
self._active_leaf_node_cnt -= 1
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)
# Manage memory
self.enforce_tracker_limit()
def _attempt_to_split(self, node: ActiveLearningNode, parent: SplitNode,
parent_idx: int):
""" Attempt to split a node.
If the samples seen so far are not from the same class then:
1. Find split candidates and select the top 2.
2. Compute the Hoeffding bound.
3. If the difference between the top 2 split candidates is larger than the Hoeffding bound:
3.1 Replace the leaf node by a split node.
3.2 Add a new leaf node on each branch of the new split node.
3.3 Update tree's metrics
Optional: Disable poor attribute. Depends on the tree's configuration.
Parameters
----------
node: ActiveLearningNode
The node to evaluate.
parent: SplitNode
The node's parent.
parent_idx: int
Parent node's branch index.
"""
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()
elif self._split_criterion == HELLINGER:
split_criterion = HellingerDistanceCriterion()
else:
split_criterion = InfoGainSplitCriterion()
best_split_suggestions = node.get_best_split_suggestions(
split_criterion, self)
best_split_suggestions.sort(key=attrgetter('merit'))
should_split = False
if len(best_split_suggestions) < 2:
should_split = len(best_split_suggestions) > 0
else:
hoeffding_bound = self.compute_hoeffding_bound(
split_criterion.get_range_of_merit(
node.get_observed_class_distribution()),
self.split_confidence, node.get_weight_seen())
best_suggestion = best_split_suggestions[-1]
second_best_suggestion = best_split_suggestions[-2]
if (best_suggestion.merit - second_best_suggestion.merit >
hoeffding_bound or hoeffding_bound < self.tie_threshold
): # best_suggestion.merit > 1e-10 and \
should_split = True
if self.remove_poor_atts is not None and self.remove_poor_atts:
poor_atts = set()
# Scan 1 - add any poor attribute to set
for i in range(len(best_split_suggestions)):
if best_split_suggestions[i] is not None:
split_atts = best_split_suggestions[
i].split_test.get_atts_test_depends_on()
if len(split_atts) == 1:
if best_suggestion.merit - best_split_suggestions[
i].merit > hoeffding_bound:
poor_atts.add(int(split_atts[0]))
# Scan 2 - remove good attributes from set
for i in range(len(best_split_suggestions)):
if best_split_suggestions[i] is not None:
split_atts = best_split_suggestions[
i].split_test.get_atts_test_depends_on()
if len(split_atts) == 1:
if best_suggestion.merit - best_split_suggestions[
i].merit < hoeffding_bound:
poor_atts.remove(int(split_atts[0]))
for poor_att in poor_atts:
node.disable_attribute(poor_att)
if should_split:
split_decision = best_split_suggestions[-1]
if split_decision.split_test is None:
# Preprune - null wins
self._deactivate_learning_node(node, parent, parent_idx)
else:
new_split = self.new_split_node(
split_decision.split_test,
node.get_observed_class_distribution())
for i in range(split_decision.num_splits()):
new_child = self._new_learning_node(
split_decision.
resulting_class_distribution_from_split(i))
new_split.set_child(i, new_child)
self._active_leaf_node_cnt -= 1
self._decision_node_cnt += 1
self._active_leaf_node_cnt += split_decision.num_splits()
if parent is None:
self._tree_root = new_split
else:
parent.set_child(parent_idx, new_split)
# Manage memory
self.enforce_tracker_limit()
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