22:45:17 2017-08-09
KNN算法简单有效，可以解决很多分类问题。但是无法给出数据的含义，就是一顿计算向量距离，然后分类。
决策树就可以解决这个问题，分类之后能够知道是问什么被划分到一个类。用图形画出来就效果更好了，这次没有学哪个画图的，下次。
这里只涉及信息熵的计算，最佳分类特征的提取，决策树的构建。剪枝没有学，这里没有。
1 # -*- oding: itf-8 -*-
2
3 ‘‘‘
4 function: 《机器学习实战》决策树的代码，画图的部分没有写；
5 note: 贴出来以后用方便一点~
6 date: 2017.8.9
7 ‘‘‘
8
9 from numpy import *
10 from math import log
11 import operator
12
13 #计算香浓信息熵
14 def calcuEntropy(dataSet):
15 numOfEntries = len(dataSet)
16 featVec = {}
17 for data in dataSet:
18 currentLabel = data[-1]
19 if currentLabel not in featVec.keys():
20 featVec[currentLabel] = 1
21 else:
22 featVec[currentLabel] += 1
23 shannonEntropy = 0.0
24 for feat in featVec.keys():
25 prob = float(featVec[feat]) / numOfEntries
26 shannonEntropy += -prob*log(prob, 2)
27 return shannonEntropy
28
29 #产生数据集
30 def loadDataSet():
31 dataSet = [[1,1,‘yes‘],
32 [1,0,‘no‘],
33 [0,1,‘no‘],
34 [0,1,‘no‘]]
35 labels = [‘no surfacing‘, ‘flippers‘]
36 return dataSet, labels
37
38 ‘‘‘
39 function: split the dataset
40 return: 基于划分特征划分之后我们想要的那部分集合
41 parameters: dataSet: 数据集，axis: 要划分的特征, value:要返回的集合的axis特征值
42 ‘‘‘
43 def splitDataSet(dataSet, axis, value):
44 retDataSet = [] #防止原始的数据集被修改
45 for featVec in dataSet:
46 if featVec[axis] == value: #我们想要的数值存起来，一会返回
47 reducedFeatVec = featVec[:axis]
48 reducedFeatVec.extend(featVec[axis+1:])
49 retDataSet.append(reducedFeatVec)
50 return retDataSet
51
52 ‘‘‘
53 function: 找出数据集中最佳的划分特征
54 ‘‘‘
55 def chooseBestClassifyFeat(dataSet):
56 numOfFeatures = len(dataSet[0]) - 1
57 bestFeature = -1 #初始化最佳的划分特征
58 baseInfoGain = 0.0 #信息增益
59 baseEntropy = calcuEntropy(dataSet)
60 for i in range(numOfFeatures):
61 # if numOfFeatures == 1: #错了，只有一个特征不是只有一个类别
62 # print(‘only one feature‘)
63 # print(dataSet[0][0])
64 # return dataSet[0][0] #只有一个特征直接返回该特征
65 featList = [example[i] for example in dataSet] #或者第i个特征所有的取值
66 unicVals = set(featList) #不重复的第i个特征取值
67 newEntropy = 0.0
68 for value in unicVals:
69 subDataSet = splitDataSet(dataSet, i, value)
70
71 #计算划分之后各个子数据集的信息熵，然后累加就是这个划分的信息熵
72 currentEntropy = calcuEntropy(subDataSet)
73 prob = float(len(subDataSet)) / len(dataSet)
74 newEntropy += prob * currentEntropy
75 newInfoGain = baseEntropy - newEntropy
76 if newInfoGain > baseInfoGain:
77 bestFeature = i
78 baseInfoGain = newInfoGain
79 return bestFeature
80
81 ‘‘‘
82 function: 多数表决，当分类器用完所有属性，叶节点还是类别不统一的时候调用这个函数
83 arg: labelList 类别标签列表
84 ‘‘‘
85 def majorityCount(labelList):
86 classCount = {}
87 for label in labelList:
88 if label not in classCount.keys():
89 classCount[label] = 0
90 classCount[label] += 1
91 sortedClassCount = sorted(classCount.items(), key=operator.itemgetter(1),reverse = True)
92 print(sortedClassCount)
93 return sortedClassCount[0][0]
94
95
96 ‘‘‘
97 function: 递归的建造决策树
98 arg: dataset: 数据集 labels: 代表特征的标签，起始算法不需要,比如fippers代表第一个特征的意义
99 ‘‘‘
100 def createTree(dataSet, labels):
101 classList = [example[-1] for example in dataSet] #得到所有的类别
102 if classList.count(classList[0]) == len(classList): #只有一种类别，直接返回
103 return classList[0]
104 if len(dataSet[0]) == 1: #特征属性用完了但是还没有完全分开，多数表决
105 return majorityCount(classList)
106 bestFeat = chooseBestClassifyFeat(dataSet)
107 print(‘bestFeat = ‘ + str(bestFeat))
108 bestFeatLabel = labels[bestFeat]
109 del(labels[bestFeat]) #删除这次使用的特征
110 featValues = [example[bestFeat] for example in dataSet]
111 myTree = {bestFeatLabel: {}}
112 unicVals = set(featValues)
113 for value in unicVals:
114 labelCopy = labels[:]
115 subDataSet = splitDataSet(dataSet, bestFeat, value)
116 myTree[bestFeatLabel][value] = createTree(subDataSet, labelCopy)
117 return myTree
118
119 ‘‘‘
120 function: 用决策树进行分类
121 arg: inputTree: 训练好的决策树，featLabels: 特征标签，testVec: 待分类的向量
122 ‘‘‘
123 def classify(inputTree, featLabel, testVec):
124 firstStr = list(inputTree.keys())[0] #python3 dict,.keys()不支持索引，必须转换一下
125 secondDict = inputTree[firstStr] #second tree
126 featIndex = featLabel.index(firstStr) #可利用index函数找到这个特征标签对饮过的特征位置
127 for key in secondDict.keys():
128 if testVec[featIndex] == key:
129 if type(secondDict[key]).__name__ == ‘dict‘: #说明下面不是叶子节点，继续分类
130 classLabel = classify(secondDict[key], featLabel, testVec)
131 else:
132 classLabel = secondDict[key] #到达叶子节点，直接返回类别标签
133 return classLabel
134
135 ‘‘‘
136 function: 使用pickle模块持久化存储决策树
137 note:
138 ‘‘‘
139 def storeTree(inputTree, filename):
140 import pickle
141 fw = open(filename, ‘wb‘)
142 pickle.dump(inputTree, fw)
143 fw.close()
144
145 ‘‘‘
146 function: 从本地文件中读取决策树
147 ‘‘‘
148 def grabTree(filename):
149 import pickle
150 fr = open(filename,‘rb‘)
151 return pickle.load(fr)
152
153 #测试信息熵的计算
154 dataSet, labels = loadDataSet()
155 shannon = calcuEntropy(dataSet)
156 print(shannon)
157
158 #测试数据集分割
159 print(dataSet)
160 retDataSet = splitDataSet(dataSet, 1, 1)
161 print(retDataSet)
162 retDataSet = splitDataSet(dataSet, 1, 0)
163 print(retDataSet)
164
165 #寻找最佳的划分特征
166 bestFeature = chooseBestClassifyFeat(dataSet)
167 print(bestFeature)
168
169 #测试多数表决
170 out = majorityCount([1,1,2,2,2,1,2,2])
171 print(out)
172
173 #创建决策大叔
174 myTree = createTree(dataSet, labels)
175 print(myTree)
176
177 #测试分类器
178 dataSet, labels = loadDataSet()
179 classLabel = classify(myTree, labels, [0,1])
180 print(classLabel)
181 classLabel = classify(myTree, labels, [1,1])
182 print(classLabel)
183
184 #持久化存储决策树
185 storeTree(myTree, ‘classifierStorage.txt‘)
186 outTree = grabTree(‘classifierStorage.txt‘)
187 print(outTree)
时间： 2024-12-23 02:49:52