# -*- coding: utf-8 -*-
"""
Created on Fri Jul 13 16:00:57 2018
"""
#coding:utf-8
from math import log
class DecisonTree:
trainData = []
trainLabel = []
featureValus = {} #每个特征所有可能的取值
def __init__(self, trainData, trainLabel, threshold):
self.loadData(trainData, trainLabel)
self.threshold = threshold
self.tree = self.createTree(range(0,len(trainLabel)), range(0,len(trainData[0])))
#加载数据
def loadData(self, trainData, trainLabel):
if len(trainData) != len(trainLabel):
raise ValueError('input error')
self.trainData = trainData
self.trainLabel = trainLabel
#计算 featureValus
for data in trainData:
for index, value in enumerate(data):
if not index in self.featureValus.keys():
self.featureValus[index] = [value]
if not value in self.featureValus[index]:
self.featureValus[index].append(value)
#计算信息熵
def caculateEntropy(self, dataset):
labelCount = self.labelCount(dataset)
size = len(dataset)
result = 0
for i in labelCount.values():
pi = i / float(size)
result -= pi * (log(pi) /log(2))
return result
#计算信息增益
def caculateGain(self, dataset, feature):
values = self.featureValus[feature] #特征feature 所有可能的取值
result = 0
for v in values:
subDataset = self.splitDataset(dataset=dataset, feature=feature, value=v)
result += len(subDataset) / float(len(dataset)) * self.caculateEntropy(subDataset)
return self.caculateEntropy(dataset=dataset) - result
#计算数据集中，每个标签出现的次数
def labelCount(self, dataset):
labelCount = {}
for i in dataset:
if trainLabel[i] in labelCount.keys():
labelCount[trainLabel[i]] += 1
else:
labelCount[trainLabel[i]] = 1
return labelCount
'''
dataset:数据集
features:特征集
'''
def createTree(self, dataset, features):
labelCount = self.labelCount(dataset)
#如果特征集为空，则该树为单节点树
#计算数据集中出现次数最多的标签
if not features:
return max(list(labelCount.items()),key = lambda x:x[1])[0]
#如果数据集中，只包同一种标签，则该树为单节点树
if len(labelCount) == 1:
return labelCount.keys()[0]
#计算特征集中每个特征的信息增益
l = map(lambda x : [x, self.caculateGain(dataset=dataset, feature=x)], features)
#选取信息增益最大的特征
feature, gain = max(l, key = lambda x: x[1])
#如果最大信息增益小于阈值，则该树为单节点树
#
if self.threshold > gain:
return max(list(labelCount.items()),key = lambda x:x[1])[0]
tree = {}
#选取特征子集
subFeatures = filter(lambda x : x != feature, features)
tree['feature'] = feature
#构建子树
for value in self.featureValus[feature]:
subDataset = self.splitDataset(dataset=dataset, feature=feature, value=value)
#保证子数据集非空
if not subDataset:
continue
tree[value] = self.createTree(dataset=subDataset, features=subFeatures)
return tree
def splitDataset(self, dataset, feature, value):
reslut = []
for index in dataset:
if self.trainData[index][feature] == value:
reslut.append(index)
return reslut
def classify(self, data):
def f(tree, data):
if type(tree) != dict:
return tree
else:
return f(tree[data[tree['feature']]], data)
return f(self.tree, data)
if __name__ == '__main__':
trainData = [
[0, 0, 0, 0],
[0, 0, 0, 1],
[0, 1, 0, 1],
[0, 1, 1, 0],
[0, 0, 0, 0],
[1, 0, 0, 0],
[1, 0, 0, 1],
[1, 1, 1, 1],
[1, 0, 1, 2],
[1, 0, 1, 2],
[2, 0, 1, 2],
[2, 0, 1, 1],
[2, 1, 0, 1],
[2, 1, 0, 2],
[2, 0, 0, 0],
]
trainLabel = [0, 0, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0]
tree = DecisonTree(trainData=trainData, trainLabel=trainLabel, threshold=0)
print tree.tree
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