def leaf_err_sum(self, cur_node, err_set):
'''
悲观剪枝，用于计算一个当前节点子树的错误率
err_num: 当一个叶子节点数据集为空时，错误节点数目就是父节点的错误节点数
'''
if len(cur_node.childNode) == 0: #叶子节点
if len(cur_node.dataset) == 0:
err_set.append(0)
else:
err_sum = get_err_sum(cur_node.cls, cur_node.dataset)
err_set.append(err_sum)
else: # 内部节点
for _, c in cur_node.childNode.items():
if len(c.childNode) == 0 and len(c.dataset) == 0:
self.leaf_err_sum(c, err_set)
else:
self.leaf_err_sum(c, err_set)
def leaf_err_sum(self, cur_node, err_set):
'''
悲观剪枝，用于计算一个当前节点子树的错误率
err_num: 当一个叶子节点数据集为空时，错误节点数目就是父节点的错误节点数
'''
if len(cur_node.childNode) == 0: #叶子节点
if len(cur_node.dataset) == 0:
err_set.append(0)
else:
err_sum = get_err_sum(cur_node.cls, cur_node.dataset)
err_set.append(err_sum)
else: # 内部节点
for _, c in cur_node.childNode.items():
if len(c.childNode) == 0 and len(c.dataset) == 0:
self.leaf_err_sum(c, err_set)
else:
self.leaf_err_sum(c, err_set)
def __prun_tree(self, cur_node):
'''剪枝'''
if len(cur_node.childNode) == 0: #叶子节点直接跳过
return
else:
cur_node.cls = get_cls_from_data(cur_node.dataset)
cur_err_sum = get_err_sum(cur_node.cls, cur_node.dataset) + 0.5
leaf_err_set = []
self.leaf_err_sum(cur_node, leaf_err_set)
leaf_e_sum = sum(leaf_err_set) + 0.5 * len(leaf_err_set)
leaf_err_ratio = leaf_e_sum / len(cur_node.dataset)
std_dev = np.sqrt(leaf_err_ratio * (1 - leaf_err_ratio))
if leaf_e_sum + std_dev > cur_err_sum:
print leaf_e_sum + std_dev, cur_err_sum, " prun!!!!"
cur_node.childNode = {}
cur_node.cls = get_cls_from_data(cur_node.dataset)
else:
for _, c in cur_node.childNode.items():
self.__prun_tree(c)
def __prun_tree(self, cur_node):
'''剪枝'''
if len(cur_node.childNode) == 0: #叶子节点直接跳过
return
else:
cur_node.cls = get_cls_from_data(cur_node.dataset)
cur_err_sum = get_err_sum(cur_node.cls, cur_node.dataset) + 0.5
leaf_err_set = []
self.leaf_err_sum(cur_node, leaf_err_set)
leaf_e_sum = sum(leaf_err_set) + 0.5 * len(leaf_err_set)
leaf_err_ratio = leaf_e_sum / len(cur_node.dataset)
std_dev = np.sqrt(leaf_err_ratio * (1 - leaf_err_ratio))
if leaf_e_sum + std_dev > cur_err_sum:
print leaf_e_sum + std_dev, cur_err_sum, " prun!!!!"
cur_node.childNode = {}
cur_node.cls = get_cls_from_data(cur_node.dataset)
else:
for _, c in cur_node.childNode.items():
self.__prun_tree(c)