一、各种熵的计算
entropy_utils.py
import numpy as np # 数值计算
import math # 标量数据的计算
class EntropyUtils:
"""
决策树中各种熵的计算，包括信息熵、信息增益、信息增益率、基尼指数。
统一要求：按照信息增益最大、信息增益率最大、基尼指数增益最大
"""
@staticmethod
def _set_sample_weight(sample_weight, n_samples):
"""
扩展到集成学习，此处为样本权重的设置
:param sample_weight: 各样本的权重
:param n_samples: 样本量
:return:
"""
if sample_weight is None:
sample_weight = np.asarray([1.0] * n_samples)
return sample_weight
def cal_info_entropy(self, y_labels, sample_weight=None):
"""
计算样本的信息熵
:param y_labels: 递归样本子集中类别集合或特征取值
:param sample_weight: 各样本的权重
:return:
"""
y = np.asarray(y_labels)
sample_weight = self._set_sample_weight(sample_weight, len(y))
y_values = np.unique(y) # 样本中不同类别值
ent_y = 0.0
for val in y_values:
p_i = len(y[y == val]) * np.mean(sample_weight[y == val]) / len(y)
ent_y += -p_i * math.log2(p_i)
return ent_y
def conditional_entropy(self, feature_x, y_labels, sample_weight=None):
"""
计算条件熵，给定特征属性的情况下，信息熵的计算
:param feature_x: 某个样本特征
:param y_labels: 递归样本子集中的类别集合
:param sample_weight: 各样本的权重
:return:
"""
x, y = np.asarray(feature_x), np.asarray(y_labels)
sample_weight = self._set_sample_weight(sample_weight, len(y))
cond_ent = 0.0
for x_val in np.unique(x):
x_idx = np.where(x == x_val) # 某个特征取值的样本索引集合
sub_x, sub_y = x[x_idx], y[x_idx]
sub_sample_weight = sample_weight[x_idx]
p_k = len(sub_y) / len(y)
cond_ent += p_k * self.cal_info_entropy(sub_y, sub_sample_weight)
return cond_ent
def info_gain(self, feature_x, y_labels, sample_weight=None):
"""
计算信息增益
:param feature_x:
:param y_labels:
:param sample_weight:
:return:
"""
return self.cal_info_entropy(y_labels, sample_weight) - \
self.conditional_entropy(feature_x, y_labels, sample_weight)
def info_gain_rate(self, feature_x, y_labels, sample_weight=None):
"""
计算信息增益率
:param feature_x:
:param y_labels:
:param sample_weight:
:return:
"""
return self.info_gain(feature_x, y_labels, sample_weight) / \
self.cal_info_entropy(feature_x, sample_weight)
def cal_gini(self, y_label, sample_weight=None):
"""
计算当前特征或类别集合的基尼值
:param y_label: 递归样本子集中类别集合或特征取值
:param sample_weight:
:return:
"""
y = np.asarray(y_label)
sample_weight = self._set_sample_weight(sample_weight, len(y))
y_values = np.unique(y)
gini_val = 1.0
for val in y_values:
p_k = len(y[y == val]) * np.mean(sample_weight[y == val]) / len(y)
gini_val -= p_k ** 2
return gini_val
def conditional_gini(self, feature_x, y_labels, sample_weight=None):
"""
计算条件基尼指数
:param feature_x:
:param y_labels:
:param sample_weight:
:return:
"""
x, y = np.asarray(feature_x), np.asarray(y_labels)
sample_weight = self._set_sample_weight(sample_weight, len(y))
cond_gini = 0.0
for x_val in np.unique(x):
x_idx = np.where(x == x_val) # 某个特征取值的样本索引集合
sub_x, sub_y = x[x_idx], y[x_idx]
sub_sample_weight = sample_weight[x_idx]
p_k = len(sub_y) / len(y)
cond_gini += p_k * self.cal_gini(sub_y, sub_sample_weight)
return cond_gini
def gini_gain(self, feature_x, y_labels, sample_weight=None):
"""
计算基尼指数增益
:param feature_x:
:param y_labels:
:param sample_weight:
:return:
"""
return self.cal_gini(y_labels, sample_weight) - \
self.conditional_gini(feature_x, y_labels, sample_weight)
# if __name__ == '__main__':
# y = np.random.randint(0, 2, 50)
# entropy = EntropyUtils()
# ent = entropy.cal_info_entropy(y)
# print(ent)
二、连续特征数据的离散分箱
data_bin_wrapper.py
import numpy as np
class DataBinsWrapper:
"""
连续特征数据的离散化，分箱（分段）操作，根据用户传参max_bins，计算分位数，以分位数分箱（分段）
然后根据样本特征取值所在区间段（哪个箱）位置索引标记当前值
1. fit(x)根据样本进行分箱
2. transform(x)根据已存在的箱，把数据分成max_bins类
"""
def __init__(self, max_bins=10):
self.max_bins = max_bins # 分箱数：10%，20%，...，90%
self.XrangeMap = None # 箱（区间段）
def fit(self, x_samples):
"""
根据样本进行分箱
:param x_samples: 样本（二维数组 n * k），或一个特征属性的数据（二维 n * 1）
:return:
"""
if x_samples.ndim == 1: # 一个特征属性，转换为二维数组
n_features = 1
x_samples = x_samples[:, np.newaxis] # 添加一个轴，转换为二维数组
else:
n_features = x_samples.shape[1]
# 构建分箱，区间段
self.XrangeMap = [[] for _ in range(n_features)]
for idx in range(n_features):
x_sorted = sorted(x_samples[:, idx]) # 按特征索引取值，并从小到大排序
for bin in range(1, self.max_bins):
p = (bin / self.max_bins) * 100 // 1
p_val = np.percentile(x_sorted, p)
self.XrangeMap[idx].append(p_val)
self.XrangeMap[idx] = sorted(list(set(self.XrangeMap[idx])))
def transform(self, x_samples, XrangeMap=None):
"""
根据已存在的箱，把数据分成max_bins类
:param x_samples: 样本（二维数组 n * k），或一个特征属性的数据（二维 n * 1）
:return:
"""
if x_samples.ndim == 1:
if XrangeMap is not None:
return np.asarray(np.digitize(x_samples, XrangeMap[0])).reshape(-1)
else:
return np.asarray(np.digitize(x_samples, self.XrangeMap[0])).reshape(-1)
else:
return np.asarray([np.digitize(x_samples[:, i], self.XrangeMap[i])
for i in range(x_samples.shape[1])]).T
# if __name__ == '__main__':
# x = np.random.randn(10, 5)
# print(x)
# dbw = DataBinsWrapper(max_bins=5)
# dbw.fit(x)
# print(dbw.XrangeMap)
# print(dbw.transform(x))三、可视化分类边界函数
plt_decision_funtion.py
import matplotlib.pylab as plt
import numpy as np
def plot_decision_function(X, y, clf, acc=None, title_info=None, is_show=True, support_vectors=None):
"""
可视化分类边界函数
:param X, y: 测试样本与类别
:param clf: 分类模型
:param acc: 模型分类正确率
:param title_info: 可视化标题title的额外信息
:param is_show: 是否在当前显示图像，用于父函数绘制子图
:param support_vectors: 扩展支持向量机
:return:
"""
if is_show:
plt.figure(figsize=(7, 5))
# 根据特征变量的最小值和最大值，生成二维网络，用于绘制等值线
x_min, x_max = X[:, 0].min() - 1, X[:, 0].max() + 1
y_min, y_max = X[:, 1].min() - 1, X[:, 1].max() + 1
xi, yi = np.meshgrid(np.arange(x_min, x_max, 0.02),
np.arange(y_min, y_max, 0.02))
y_pred = clf.predict(np.c_[xi.ravel(), yi.ravel()]) # 模型预测值
y_pred = y_pred.reshape(xi.shape)
plt.contourf(xi, yi, y_pred, alpha=0.4)
plt.scatter(X[:, 0], X[:, 1], alpha=0.8, c=y, edgecolors="k")
plt.xlabel("Feature 1", fontdict={"fontsize": 12})
plt.ylabel("Feature 2", fontdict={"fontsize": 12})
if acc:
if title_info:
plt.title("Model Classification Boundary %s \n(accuracy = %.5f)"
% (title_info, acc), fontdict={"fontsize": 14})
else:
plt.title("Model Classification Boundary (accuracy = %.5f)"
% acc, fontdict={"fontsize": 14})
else:
if title_info:
plt.title("Model Classification Boundary %s"
% title_info, fontdict={"fontsize": 14})
else:
plt.title("Model Classification Boundary", fontdict={"fontsize": 14})
if support_vectors is not None: # 可视化支持向量，针对SVM
plt.scatter(X[support_vectors, 0], X[support_vectors, 1],
s=50, c="None", alpha=0.7, edgecolors="red")
if is_show:
plt.show()
四、熵计算的测试
test_entropy.py
import numpy as np
import pandas as pd
from utils.entropy_utils import EntropyUtils
from utils.data_bin_wrapper import DataBinsWrapper
data = pd.read_csv("data/watermelon.csv").iloc[:, 1:]
feat_names = data.columns[:6]
y = data.iloc[:, -1]
ent_obj = EntropyUtils()
print("各特征的信息增益如下：")
for feat in feat_names:
print(feat, ":", ent_obj.info_gain(data.loc[:, feat], y))
print("=" * 60)
print("各特征的信息增益率如下：")
for feat in feat_names:
print(feat, ":", ent_obj.info_gain_rate(data.loc[:, feat], y))
print("=" * 60)
print("各特征的基尼指数增益如下：")
for feat in feat_names:
print(feat, ":", ent_obj.gini_gain(data.loc[:, feat], y))
print("=" * 60)
x1 = np.asarray(data.loc[:, ["密度", "含糖率"]])
print(x1)
dbw = DataBinsWrapper(max_bins=8)
dbw.fit(x1)
print(dbw.transform(x1))
五、树的结点信息封装
tree_node.py
class TreeNode_C:
"""
决策树分类算法，树的结点信息封装，实体类：setXXX()、getXXX()
"""
def __init__(self, feature_idx: int = None, feature_val=None, criterion_val: float = None,
n_samples: int = None, target_dist: dict = None, weight_dist: dict = None,
left_child_Node=None, right_child_Node=None):
"""
决策树结点信息封装
:param feature_idx: 特征索引，如果指定特征属性的名称，可以按照索引取值
:param feature_val: 特征取值
:param criterion_val: 划分结点的标准：信息增益（率）、基尼指数增益
:param n_samples: 当前结点所包含的样本量
:param target_dist: 当前结点类别分布：0-25%，1-50%，2-25%
:param weight_dist: 当前结点所包含的样本权重分布
:param left_child_Node: 左子树
:param right_child_Node: 右子树
"""
self.feature_idx = feature_idx
self.feature_val = feature_val
self.criterion_val = criterion_val
self.n_samples = n_samples
self.target_dist = target_dist
self.weight_dist = weight_dist
self.left_child_Node = left_child_Node # 递归
self.right_child_Node = right_child_Node # 递归
def level_order(self):
"""
按层次遍历树...
:return:
"""
pass
# def get_feature_idx(self):
# return self.get_feature_idx()
#
# def set_feature_idx(self, feature_idx):
# self.feature_idx = feature_idx
六、分类决策树算法的实现
decision_tree_C.py
import numpy as np
from utils.entropy_utils import EntropyUtils
from utils.tree_node import TreeNode_C
from utils.data_bin_wrapper import DataBinsWrapper
class DecisionTreeClassifier:
"""
分类决策树算法实现：无论是ID3、C4.5或CART，统一按照二叉树构造
1. 划分标准：信息增益（率）、基尼指数增益，都按照最大值选择特征属性
2. 创建决策树fit()，递归算法实现，注意出口条件
3. 预测predict_proba()、predict() --> 对树的搜索
4. 数据的预处理操作，尤其是连续数据的离散化，分箱
5. 剪枝处理
"""
def __init__(self, criterion="CART", is_feature_all_R=False, dbw_feature_idx=None,
max_depth=None, min_sample_split=2, min_sample_leaf=1,
min_impurity_decrease=0, max_bins=10):
self.utils = EntropyUtils() # 结点划分类
self.criterion = criterion # 结点的划分标准
if criterion.lower() == "cart":
self.criterion_func = self.utils.gini_gain # 基尼指数增益
elif criterion.lower() == "c45":
self.criterion_func = self.utils.info_gain_rate # 信息增益率
elif criterion.lower() == "id3":
self.criterion_func = self.utils.info_gain # 信息增益
else:
raise ValueError("参数criterion仅限cart、c45或id3...")
self.is_feature_all_R = is_feature_all_R # 所有样本特征是否全是连续数据
self.dbw_feature_idx = dbw_feature_idx # 混合类型数据，可指定连续特征属性的索引
self.max_depth = max_depth # 树的最大深度，不传参，则一直划分下去
self.min_sample_split = min_sample_split # 最小的划分结点的样本量，小于则不划分
self.min_sample_leaf = min_sample_leaf # 叶子结点所包含的最小样本量，剩余的样本小于这个值，标记叶子结点
self.min_impurity_decrease = min_impurity_decrease # 最小结点不纯度减少值，小于这个值，不足以划分
self.max_bins = max_bins # 连续数据的分箱数，越大，则划分越细
self.root_node: TreeNode_C() = None # 分类决策树的根节点
self.dbw = DataBinsWrapper(max_bins=max_bins) # 连续数据离散化对象
self.dbw_XrangeMap = {} # 存储训练样本连续特征分箱的端点
self.class_values = None # 样本的类别取值
def _data_bin_wrapper(self, x_samples):
"""
针对特定的连续特征属性索引dbw_feature_idx，分别进行分箱，考虑测试样本与训练样本使用同一个XrangeMap
:param x_samples: 样本：即可以是训练样本，也可以是测试样本
:return:
"""
self.dbw_feature_idx = np.asarray(self.dbw_feature_idx)
x_samples_prop = [] # 分箱之后的数据
if not self.dbw_XrangeMap:
# 为空，即创建决策树前所做的分箱操作
for i in range(x_samples.shape[1]):
if i in self.dbw_feature_idx: # 说明当前特征是连续数值
self.dbw.fit(x_samples[:, i])
self.dbw_XrangeMap[i] = self.dbw.XrangeMap
x_samples_prop.append(self.dbw.transform(x_samples[:, i]))
else:
x_samples_prop.append(x_samples[:, i])
else: # 针对测试样本的分箱操作
for i in range(x_samples.shape[1]):
if i in self.dbw_feature_idx: # 说明当前特征是连续数值
x_samples_prop.append(self.dbw.transform(x_samples[:, i], self.dbw_XrangeMap[i]))
else:
x_samples_prop.append(x_samples[:, i])
return np.asarray(x_samples_prop).T
def fit(self, x_train, y_train, sample_weight=None):
"""
决策树的创建，递归操作前的必要信息处理
:param x_train: 训练样本：ndarray，n * k
:param y_train: 目标集：ndarray，（n， ）
:param sample_weight: 各样本的权重，（n， ）
:return:
"""
x_train, y_train = np.asarray(x_train), np.asarray(y_train)
self.class_values = np.unique(y_train) # 样本的类别取值
n_samples, n_features = x_train.shape # 训练样本的样本量和特征属性数目
if sample_weight is None:
sample_weight = np.asarray([1.0] * n_samples)
self.root_node = TreeNode_C() # 创建一个空树
if self.is_feature_all_R: # 全部是连续数据
self.dbw.fit(x_train)
x_train = self.dbw.transform(x_train)
elif self.dbw_feature_idx:
x_train = self._data_bin_wrapper(x_train)
self._build_tree(1, self.root_node, x_train, y_train, sample_weight)
# print(x_train)
def _build_tree(self, cur_depth, cur_node: TreeNode_C, x_train, y_train, sample_weight):
"""
递归创建决策树算法，核心算法。按先序（中序、后序）创建的
:param cur_depth: 递归划分后的树的深度
:param cur_node: 递归划分后的当前根结点
:param x_train: 递归划分后的训练样本
:param y_train: 递归划分后的目标集合
:param sample_weight: 递归划分后的各样本权重
:return:
"""
n_samples, n_features = x_train.shape # 当前样本子集中的样本量和特征属性数目
target_dist, weight_dist = {}, {} # 当前样本类别分布和权重分布 0-->30%，1-->70%
class_labels = np.unique(y_train) # 不同的类别值
for label in class_labels:
target_dist[label] = len(y_train[y_train == label]) / n_samples
weight_dist[label] = np.mean(sample_weight[y_train == label])
cur_node.target_dist = target_dist
cur_node.weight_dist = weight_dist
cur_node.n_samples = n_samples
# 递归出口判断
if len(target_dist) <= 1: # 所有的样本全属于同一个类别，递归出口1
# 如果为0，则表示当前样本集合为空，递归出口3
return
if n_samples < self.min_sample_split: # 当前结点所包含的样本量不足以划分
return
if self.max_depth is not None and cur_depth > self.max_depth: # 树的深度达到最大深度
return
# 划分标准，选择最佳的划分特征及其取值
best_idx, best_val, best_criterion_val = None, None, 0.0
for k in range(n_features): # 对当前样本集合中每个特征计算划分标准
for f_val in np.unique(x_train[:, k]): # 当前特征的不同取值
feat_k_values = (x_train[:, k] == f_val).astype(int) # 是当前取值f_val就是1，否则就是0
criterion_val = self.criterion_func(feat_k_values, y_train, sample_weight)
if criterion_val > best_criterion_val:
best_criterion_val = criterion_val # 最佳的划分标准值
best_idx, best_val = k, f_val # 当前最佳特征索引以及取值
# 递归出口的判断
if best_idx is None: # 当前属性为空，或者所有样本在所有属性上取值相同，无法划分
return
if best_criterion_val <= self.min_impurity_decrease: # 小于最小不纯度阈值，不划分
return
cur_node.criterion_val = best_criterion_val
cur_node.feature_idx = best_idx
cur_node.feature_val = best_val
# print("当前划分的特征索引：", best_idx, "取值：", best_val, "最佳标准值：", best_criterion_val)
# print("当前结点的类别分布：", target_dist)
# 创建左子树，并递归创建以当前结点为子树根节点的左子树
left_idx = np.where(x_train[:, best_idx] == best_val) # 左子树所包含的样本子集索引
if len(left_idx) >= self.min_sample_leaf: # 小于叶子结点所包含的最少样本量，则标记为叶子结点
left_child_node = TreeNode_C() # 创建左子树空结点
# 以当前结点为子树根结点，递归创建
cur_node.left_child_Node = left_child_node
self._build_tree(cur_depth + 1, left_child_node, x_train[left_idx],
y_train[left_idx], sample_weight[left_idx])
right_idx = np.where(x_train[:, best_idx] != best_val) # 右子树所包含的样本子集索引
if len(right_idx) >= self.min_sample_leaf: # 小于叶子结点所包含的最少样本量，则标记为叶子结点
right_child_node = TreeNode_C() # 创建右子树空结点
# 以当前结点为子树根结点，递归创建
cur_node.right_child_Node = right_child_node
self._build_tree(cur_depth + 1, right_child_node, x_train[right_idx],
y_train[right_idx], sample_weight[right_idx])
def _search_tree_predict(self, cur_node: TreeNode_C, x_test):
"""
根据测试样本从根结点到叶子结点搜索路径，判定类别
搜索：按照后续遍历
:param x_test: 单个测试样本
:return:
"""
if cur_node.left_child_Node and x_test[cur_node.feature_idx] == cur_node.feature_val:
return self._search_tree_predict(cur_node.left_child_Node, x_test)
elif cur_node.right_child_Node and x_test[cur_node.feature_idx] != cur_node.feature_val:
return self._search_tree_predict(cur_node.right_child_Node, x_test)
else:
# 叶子结点，类别，包含有类别分布
# print(cur_node.target_dist)
class_p = np.zeros(len(self.class_values)) # 测试样本的类别概率
for i, c in enumerate(self.class_values):
class_p[i] = cur_node.target_dist.get(c, 0) * cur_node.weight_dist.get(c, 1.0)
class_p / np.sum(class_p) # 归一化
return class_p
def predict_proba(self, x_test):
"""
预测测试样本x_test的类别概率
:param x_test: 测试样本ndarray、numpy数值运算
:return:
"""
x_test = np.asarray(x_test) # 避免传递DataFrame、list...
if self.is_feature_all_R:
if self.dbw.XrangeMap is not None:
x_test = self.dbw.transform(x_test)
else:
raise ValueError("请先创建决策树...")
elif self.dbw_feature_idx is not None:
x_test = self._data_bin_wrapper(x_test)
prob_dist = [] # 用于存储测试样本的类别概率分布
for i in range(x_test.shape[0]):
prob_dist.append(self._search_tree_predict(self.root_node, x_test[i]))
return np.asarray(prob_dist)
def predict(self, x_test):
"""
预测测试样本的类别
:param x_test: 测试样本
:return:
"""
x_test = np.asarray(x_test) # 避免传递DataFrame、list...
return np.argmax(self.predict_proba(x_test), axis=1)
def _prune_node(self, cur_node: TreeNode_C, alpha):
"""
递归剪枝，针对决策树中的内部结点，自底向上，逐个考察
方法：后序遍历
:param cur_node: 当前递归的决策树的内部结点
:param alpha: 剪枝阈值
:return:
"""
# 若左子树存在，递归左子树进行剪枝
if cur_node.left_child_Node:
self._prune_node(cur_node.left_child_Node, alpha)
# 若右子树存在，递归右子树进行剪枝
if cur_node.right_child_Node:
self._prune_node(cur_node.right_child_Node, alpha)
# 针对决策树的内部结点剪枝，非叶结点
if cur_node.left_child_Node is not None or cur_node.right_child_Node is not None:
for child_node in [cur_node.left_child_Node, cur_node.right_child_Node]:
if child_node is None:
# 可能存在左右子树之一为空的情况，当左右子树划分的样本子集数小于min_samples_leaf
continue
if child_node.left_child_Node is not None or child_node.right_child_Node is not None:
return
# 计算剪枝前的损失值，2表示当前结点包含两个叶子结点
pre_prune_value = 2 * alpha
for child_node in [cur_node.left_child_Node, cur_node.right_child_Node]:
# 计算左右叶子结点的经验熵
if child_node is None:
# 可能存在左右子树之一为空的情况，当左右子树划分的样本子集数小于min_samples_leaf
continue
for key, value in child_node.target_dist.items(): # 对每个叶子结点的类别分布
pre_prune_value += -1 * child_node.n_samples * value * np.log(value) * \
child_node.weight_dist.get(key, 1.0)
# 计算剪枝后的损失值，当前结点即是叶子结点
after_prune_value = alpha
for key, value in cur_node.target_dist.items(): # 当前待剪枝的结点的类别分布
after_prune_value += -1 * cur_node.n_samples * value * np.log(value) * \
cur_node.weight_dist.get(key, 1.0)
if after_prune_value <= pre_prune_value: # 进行剪枝操作
cur_node.left_child_Node = None
cur_node.right_child_Node = None
cur_node.feature_idx, cur_node.feature_val = None, None
def prune(self, alpha=0.01):
"""
决策树后剪枝算法（李航）C(T) + alpha * |T|
:param alpha: 剪枝阈值，权衡模型对训练数据的拟合程度与模型的复杂度
:return:
"""
self._prune_node(self.root_node, alpha)
return self.root_node
七、分类决策树算法的测试
test_decision_tree_C.py
import pandas as pd
from decision_tree_C import DecisionTreeClassifier
from sklearn.datasets import load_iris, load_breast_cancer
from sklearn.model_selection import train_test_split
from sklearn.metrics import classification_report, accuracy_score
import numpy as np
import matplotlib.pyplot as plt
from sklearn.preprocessing import LabelEncoder
# data = pd.read_csv("data/watermelon.csv").iloc[:, 1:]
# X = data.iloc[:, :-1]
# y = data.iloc[:, -1]
# iris = load_iris()
# X, y = iris.data, iris.target
# bc_data = load_breast_cancer()
# X, y = bc_data.data, bc_data.target
nursery = pd.read_csv("data/nursery.csv").dropna()
X, y = np.asarray(nursery.iloc[:, :-1]), np.asarray(nursery.iloc[:, -1])
y = LabelEncoder().fit_transform(y)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=0, stratify=y)
depth = np.linspace(2, 12, 11, dtype=np.int64)
accuracy = []
for d in depth:
dtc = DecisionTreeClassifier(is_feature_all_R=False, max_depth=d)
dtc.fit(X_train, y_train)
y_pred_labels = dtc.predict(X_test)
acc = accuracy_score(y_test, y_pred_labels)
# print(acc)
accuracy.append(acc)
# dtc = DecisionTreeClassifier(dbw_feature_idx=[6, 7], max_bins=8, max_depth=2)
# dtc.fit(X, y)
# y_pred_prob = dtc.predict_proba(X)
# print(y_pred_prob)
# print(classification_report(y_test, y_pred_labels))
plt.figure(figsize=(7, 5))
plt.plot(depth, accuracy, "ko-", lw=1)
plt.show()
test_decision_tree_C_2.py
import numpy as np
import matplotlib.pyplot as plt
from decision_tree_C import DecisionTreeClassifier
from sklearn.datasets import make_classification
from sklearn.metrics import classification_report, accuracy_score
from utils.plt_decision_function import plot_decision_function
# 生成数据
data, target = make_classification(n_samples=100, n_features=2, n_classes=2, n_informative=1, n_redundant=0,
n_clusters_per_class=1, class_sep=0.8, random_state=21)
# print(data)
# print(target)
cart_tree = DecisionTreeClassifier(is_feature_all_R=True)
cart_tree.fit(data, target)
y_test_pred = cart_tree.predict(data)
print(classification_report(target, y_test_pred))
plt.figure(figsize=(14, 10))
plt.subplot(221)
acc = accuracy_score(target, y_test_pred)
plot_decision_function(data, target, cart_tree, acc=acc, is_show=False, title_info="By CART UnPrune")
# 剪枝处理
alpha = [1, 3, 5]
for i in range(3):
cart_tree.prune(alpha=alpha[i])
y_test_pred = cart_tree.predict(data)
acc = accuracy_score(target, y_test_pred)
plt.subplot(222 + i)
plot_decision_function(data, target, cart_tree, acc=acc, is_show=False,
title_info="By CART Prune α = %.1f" % alpha[i])
plt.tight_layout()
plt.show()
test_decision_tree_C_3.py
import copy
import numpy as np
import matplotlib.pyplot as plt
from decision_tree_C import DecisionTreeClassifier
from sklearn.datasets import load_breast_cancer, load_iris
from sklearn.metrics import classification_report, accuracy_score
from utils.plt_decision_function import plot_decision_function
from sklearn.model_selection import StratifiedKFold
bc_data = load_breast_cancer()
X, y = bc_data.data, bc_data.target
alphas = np.linspace(0, 10, 30)
accuracy_scores = [] # 存储每个alpha阈值下的交叉验证均分
cart = DecisionTreeClassifier(criterion="cart", is_feature_all_R=True, max_bins=10)
for alpha in alphas:
scores = []
k_fold = StratifiedKFold(n_splits=10).split(X, y)
for train_idx, test_idx in k_fold:
tree = copy.deepcopy(cart)
tree.fit(X[train_idx], y[train_idx])
tree.prune(alpha=alpha)
y_test_pred = tree.predict(X[test_idx])
scores.append(accuracy_score(y[test_idx], y_test_pred))
del tree
print(alpha, ":", np.mean(scores))
accuracy_scores.append(np.mean(scores))
plt.figure(figsize=(7, 5))
plt.plot(alphas, accuracy_scores, "ko-", lw=1)
plt.grid(ls=":")
plt.xlabel("Alpha", fontdict={"fontsize": 12})
plt.ylabel("Accuracy Scores", fontdict={"fontsize": 12})
plt.title("Cross Validation Scores under different Prune Alpha", fontdict={"fontsize": 14})
plt.show()
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