def tdidt(self, current_instances, available_attributes):
# basic approach (uses recursion!!):
# select an attribute to split on
split_attribute = myutils.select_attribute(current_instances,
available_attributes,
self.header)
available_attributes.remove(split_attribute)
# cannot split on the same attribute twice in a branch
# recall: python is pass by object reference!!
tree = ["Attribute", split_attribute]
prevPartition = current_instances
# group data by attribute domains (creates pairwise disjoint partitions)
partitions = self.partition_instances(current_instances,
split_attribute)
# for each partition, repeat unless one of the following occurs (base case)
for attribute_value, partition in partitions.items():
value_subtree = ["Value", attribute_value]
# TODO: appending leaf nodes and subtrees appropriately to value_subtree
# CASE 1: all class labels of the partition are the same => make a leaf node
if len(partition) > 0 and myutils.all_same_class(partition):
value_subtree.append([
"Leaf", partition[0][-1],
len(partition),
len(current_instances)
])
# CASE 2: no more attributes to select (clash) => handle clash w/majority vote leaf node
elif len(partition) > 0 and len(available_attributes) == 0:
[majority, count,
total] = myutils.compute_partition_stats(partition)
value_subtree.append(["Leaf", majority, count, total])
# CASE 3: no more instances to partition (empty partition) => backtrack and replace attribute node with majority vote leaf node
elif len(partition) == 0:
[majority, count,
total] = myutils.compute_partition_stats(prevPartition)
value_subtree.append(["Leaf", majority, count, total])
else: # all base cases are false... recurse!!
if len(available_attributes) > self.F:
subtree = self.tdidt(
partition,
random.sample(available_attributes.copy(), self.F))
else:
subtree = self.tdidt(partition,
available_attributes.copy())
value_subtree.append(subtree)
tree.append(value_subtree)
# need to append subtree to value_subtree and appropriately append value subtree to tree
return tree
def tdidt(self, current_instances, available_attributes):
# select an attribute to split on
split_attribute = myutils.select_attribute(current_instances, available_attributes,
self.attribute_domains, self.header)
available_attributes.remove(split_attribute)
# cannot split on the same attribute twice in a branch
# recall: python is pass by object reference!!
tree = ["Attribute", split_attribute]
# group data by attribute domains (creates pairwise disjoint partitions)
partitions = myutils.partition_instances(current_instances, split_attribute,
self.attribute_domains, self.header)
# for each partition, repeat unless one of the following occurs (base case)
for attribute_value, partition in partitions.items():
value_subtree = ["Value", attribute_value]
# CASE 1: all class labels of the partition are the same => make a leaf node
if len(partition) > 0 and myutils.all_same_class(partition):
leaf_node = myutils.create_leaf_node(partition, partitions, case = 1)
value_subtree.append(leaf_node)
tree.append(value_subtree)
# CASE 2: no more attributes to select (clash) => handle clash w/majority vote leaf node
elif len(partition) > 0 and len(available_attributes) == 0:
leaf_node = myutils.create_leaf_node(partition, partitions, case = 2)
value_subtree.append(leaf_node)
tree.append(value_subtree)
# CASE 3: no more instances to partition (empty partition) => backtrack and replace attribute node with majority vote leaf node
elif len(partition) == 0:
# replace attribute node with majority vote leaf node
# tree = create_leaf_node(partition, partitions, case = 3)
# break # don't look at the other attributes because we are replacing attribute node with leaf node
return None
else: # all base cases are false... recurse!!
subtree = self.tdidt(partition, available_attributes.copy())
# check if previous step was a case 3
# create a majority vote node if so
if subtree is None:
leaf_node = myutils.create_leaf_node(partition, partitions, case = 2)
value_subtree.append(leaf_node)
else:
# need to append subtree to value_subtree and appropriately append value subtre
# to tree
# subtree is 3rd value in list
value_subtree.append(subtree)
tree.append(value_subtree)
return tree