朴素贝叶斯

最新推荐文章于 2021-02-20 15:00:23 发布

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使用概率分布进行分类，根据概率大小决定分类结果

有标签的数据分类，构建词向量和标签

def loadDataSet():
    postingList =[['my', 'dog', 'has', 'flea', 'problems', 'help', 'please'],
                  ['maybe', 'not', 'take', 'him', 'to', 'dog', 'park', 'stupid'],
                  ['my', 'dalmation', 'is', 'so', 'cute', 'I', 'love', 'him'],
                  ['stop', 'posting', 'stupid', 'worthless', 'garbage'],
                  ['mr', 'licks', 'ate', 'my', 'steak', 'how', 'to', 'stop', 'him'],
                  ['quit', 'buying', 'worthless', 'dog', 'food', 'stupid']]
    classVec = [0, 1, 0, 1, 0, 1]
    return postingList, classVec

创建词汇表，词汇表中包含文本的所有词汇

# 创建包含在所有文档中出现的不重复词列表
def createVocabList(dataSet):
    # set去重复，无序
    vocabSet = set([])
    for document in dataSet:
        # | 用于求俩个集合的并集
        vocabSet = vocabSet | set(document)
    return list(vocabSet)

# 将输入的文档转化为与词汇表等长的向量
def setOfWordsToVec(vocabList, inputSet):
    returnVec = [0] * len(vocabList)
    for word in inputSet:
        if word in vocabList:
            returnVec[vocabList.index(word)] = 1
        else:
            print("The word: %s is not in my vocabulary" % word)
    return returnVec

对测试的文本进行处理，即将测试文本转化为与词汇表等长的向量，结果为一串0，1组成的列表

# 将输入的文档转化为与词汇表等长的向量
def setOfWordsToVec(vocabList, inputSet):
    returnVec = [0] * len(vocabList)
    for word in inputSet:
        if word in vocabList:
            returnVec[vocabList.index(word)] = 1
        else:
            print("The word: %s is not in my vocabulary" % word)
    return returnVec

利用朴素贝叶斯计算不同类别下的概率

# 朴素贝叶斯分类器训练函数
def trainNB0(trainMatrix, trainCategory):
    # 总文档数
    numTrainDocs = len(trainMatrix)
    # print(numTrainDocs)
    # 词条总数（词汇表的词汇个数）
    numWords = len(trainMatrix[0])
    # print(numWords)
    # 文档属于侮辱性文档的概率
    pAbusive = sum(trainCategory) / float(numTrainDocs)
    # 按照词汇表大小初始化
    p0Num = ones(numWords)
    # print(p0Num)
    p1Num = ones(numWords)
    # 初始化每个类别总数
    p0Denom = 2.0
    p1Denom = 2.0
    # 对每个文档循环
    for i in range(numTrainDocs):
        if trainCategory[i] == 1:
            # 对于属于侮辱性的每篇文档，如果某个词在该文档中出现，则对应位置增加1，侮辱性文档的词条数目加1
            p1Num += trainMatrix[i]
            # print(p1Num)
            p1Denom += sum(trainMatrix[i])
            # print(p1Denom)
        else:
            p0Num += trainMatrix[i]
            p0Denom += sum(trainMatrix[i])
    """
    p1Vect = p1Num / p1Denom
    p0Vect = p0Num / p0Denom
    """
    # 使用自然对数，避免下溢出或者浮点数舍入错误（采用自然对数进行处理不会有损失）
    p1Vect = log(p1Num / p1Denom)
    p0Vect = log(p0Num / p0Denom)
    return p0Vect, p1Vect, pAbusive

# 朴素贝叶斯分类函数，vec2Classify表示要分类的向量
def classifyNB(vec2Classify, p0Vec, p1Vec, pClass1 ):
    p1 = sum(vec2Classify * p1Vec) + log(pClass1)
    p0 = sum(vec2Classify * p0Vec) + log(1.0 - pClass1)
    if p1 > p0:
        return 1
    else:
        return 0

# 封装前面的函数，简化操作
def testingNB():
    listOPosts , listClasses = loadDataSet()
    myVocabList = createVocabList(listOPosts)
    trainMat = []
    for postinDoc in listOPosts:
        trainMat.append(setOfWordsToVec(myVocabList, postinDoc))
    p0V ,p1V, pAb = trainNB0(array(trainMat), array(listClasses))
    testEntry = ['love', 'my', 'dalmation']
    thisDoc = array(setOfWordsToVec(myVocabList, testEntry))
    print(testEntry, 'classify as :', classifyNB(thisDoc, p0V, p1V, pAb))


# testingNB()

# 词袋模型，与setOfWordsToVec()所不同的是，词袋模型，每出现一个单词，增加词向量中的对应值，而不是将该值设为1
def bagOfWordsToVec(vocabList, inputSet):
    returnVec = [0] * len(vocabList)
    for word in inputSet:
        if word in vocabList:
            returnVec[vocabList.index(word)] += 1
    return returnVec

# 使用朴素贝叶斯过滤垃圾邮件
# 将大写的字符串转化为字符串列表，去掉少于俩个字符的字符串，将所有的字符串转化为小写
def textParse(bigString):
    # 使用正则表达式切分，分隔符是除单词，数字外的任意字符串
    import re
    listOfTokens = re.split('\W*', bigString)
    return [tok.lower() for tok in listOfTokens if len(tok) > 2]


# 贝叶斯垃圾邮件分类器
def spamTest():
    docList = []
    classList = []
    fullText = []
    # 将ham和spam中的内容解析为词列表，并给垃圾邮件和非垃圾邮件分类
    for i in range(1, 26):
        wordList = textParse(open('E:\机器学习\machinelearninginaction\Ch04\email\spam\%d.txt' % i).read())
        docList.append(wordList)
        fullText.extend(wordList)
        classList.append(1)
        wordList = textParse(open('E:/机器学习/machinelearninginaction/Ch04/email/ham/%d.txt' % i, encoding='gb18030', errors='ignore').read())
        docList.append(wordList)
        fullText.extend(wordList)
        classList.append(0)
    # 创建不重复词的词列表
    vocabList = createVocabList(docList)
    # 一共有五十份邮件，初始化训练集为50
    trainingSet = list(range(50))
    testSet = []
    # 随机选择测试集，并将选择好的测试文档从训练集中删除
    for i in range(10):
        randIndex = int(random.uniform(0, len(trainingSet)))
        testSet.append(trainingSet[randIndex])
        del trainingSet[randIndex]
    # 训练集
    trainMat = []
    trainClasses = []
    for docIndex in trainingSet:
        trainMat.append(setOfWordsToVec(vocabList, docList[docIndex]))
        trainClasses.append(classList[docIndex])
    p0V, p1V, pSpam = trainNB0(array(trainMat), array(trainClasses))
    # 计算错误率
    errorCount = 0.0
    for docIndex in testSet:
        wordVector = setOfWordsToVec(vocabList, docList[docIndex])
        if classifyNB(array(wordVector), p0V, p1V, pSpam) != classList[docIndex]:
            errorCount += 1
    print("错误率", float(errorCount) / len(testSet))

导入Rss源，从个人广告中获取区域倾向

import feedparser
from chapter4.bayes import textParse
from chapter4.bayes import createVocabList
from numpy import *
from chapter4.bayes import bagOfWordsToVec
from chapter4.bayes import trainNB0
from chapter4.bayes import classifyNB


# 统计词汇表中的每个词在文本中出现的次数，返回出现次数最多的三十个词
def calcMostFreq(vocabList, fullText):
    import operator
    freqDict = {}
    for token in vocabList:
        freqDict[token] = fullText.count(token)
    sortedFreq = sorted(freqDict.items(), key=operator.itemgetter(1), reverse=True)
    return sortedFreq[:30]


# 使用俩个Rss源作为参数，交叉验证，计算错误率
def localWords(feed1, feed0):
    import feedparser
    docList = []
    classList = []
    fullText = []
    minLen = min(len(feed1['entries']), len(feed0['entries']))
    for i in range(minLen):
        wordList = textParse(feed1['entries'][i]['summary'])
        docList.append(wordList)
        fullText.extend(wordList)
        classList.append(1)
        wordList = textParse(feed0['entries'][i]['summary'])
        docList.append(wordList)
        fullText.extend(wordList)
        classList.append(0)
    vocabList = createVocabList(docList)
    top30Words = calcMostFreq(vocabList, fullText)
    # 去掉高频词汇，语言中的冗余和结构辅助性内容占据了词汇表的很大一部分，这些词对训练没有好处
    for pairW in top30Words:
        if pairW[0] in vocabList:
            vocabList.remove(pairW[0])
    trainingSet = list(range(2 * minLen))
    testSet = []
    for i in range(20):
        randIndex = int(random.uniform(0, len(trainingSet)))
        testSet.append(trainingSet[randIndex])
        del trainingSet[randIndex]
    trainMat = []
    trainClasses = []
    for docIndex in trainingSet:
        trainMat.append(bagOfWordsToVec(vocabList, docList[docIndex]))
        trainClasses.append(classList[docIndex])
    p0V, p1V, pAb = trainNB0(array(trainMat), array(trainClasses))
    errorCount = 0.0
    for docIndex in testSet:
        wordVector = bagOfWordsToVec(vocabList, docList[docIndex])
        if classifyNB(array(wordVector), p0V, p1V, pAb) != classList[docIndex]:
            errorCount += 1
    print("错误率", errorCount)
    return vocabList, p0V, p1V


"""
xa = feedparser.parse('http://xian.craigslist.org/stp/index.rss')
nj = feedparser.parse('http://nanjing.craigslist.org/stp/index.rss')
vocablist, p0V, p1V = localWords(xa, nj)
"""

# 根据某个词出现的条件概率，选择出大于某个阈值的所有词
def getTopWords(local1, local2):
    import operator
    vocabList, p0V, p1V = localWords(local1, local2)
    top1 = []
    top2 = []
    for i in range(len(p0V)):
        if p0V[i] > -6.0:
            top1.append((vocabList[i], p0V[i]))
        if p1V[i] > -6.0:
            top2.append((vocabList[i], p1V[i]))
        # 列表数组从0开始，所以按照第二个元素进行排序，即按照条件概率的大小从大到小排序
    sorted1 = sorted(top1, key=lambda pair: pair[1], reverse=True)
    print("---------------------")
    for item in sorted1:
        # 打印词汇
        print(item[0])
    sorted2 = sorted(top2, key=lambda pair: pair[1], reverse=True)
    print("--------------------")
    for item in sorted2:
        print(item[0])