機(jī)器學(xué)習(xí)實戰(zhàn)中，樸素貝葉斯那一章節(jié)只實現(xiàn)了二分類，網(wǎng)上大多數(shù)博客也只是照搬書上的源碼，沒有弄懂實現(xiàn)的根本。在此梳理了一遍樸素貝葉斯的原理，實現(xiàn)了5分類的例子，也是自己的一點(diǎn)心得，交流一下。

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from numpy import *

'''

貝葉斯公式 p(ci|w) = p(w|ci)*p(ci) / p(w)

即比較兩類別分子大小，把結(jié)果歸為分子大的一類

p(w|ci)條件概率，即在類別1或0下，w(詞頻)出現(xiàn)的概率(詞頻/此類別總詞數(shù)即n/N)

'''

# 取得DataSet中不重復(fù)的word

def createVocabList(dataSet):

vocabSet = set([])#使用set創(chuàng)建不重復(fù)詞表庫

for document in dataSet:

vocabSet = vocabSet | set(document) #創(chuàng)建兩個集合的并集

return list(vocabSet)

'''

我們將每個詞的出現(xiàn)與否作為一個特征，這可以被描述為詞集模型(set-of-words model)。

在詞集中，每個詞只能出現(xiàn)一次。

'''

def setOfWords2Vec(vocabList, inputSet):

returnVec = [0]*len(vocabList)#創(chuàng)建一個所包含元素都為0的向量

#遍歷文檔中的所有單詞，如果出現(xiàn)了詞匯表中的單詞，則將輸出的文檔向量中的對應(yīng)值設(shè)為1

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

'''

如果一個詞在文檔中出現(xiàn)不止一次，這可能意味著包含該詞是否出現(xiàn)在文檔中所不能表達(dá)的某種信息,

這種方法被稱為詞袋模型(bag-of-words model)。

在詞袋中，每個單詞可以出現(xiàn)多次。

為適應(yīng)詞袋模型，需要對函數(shù)setOfWords2Vec稍加修改，修改后的函數(shù)稱為bagOfWords2VecMN

'''

def bagOfWords2Vec(vocabList, inputSet):

returnVec = [0]*len(vocabList)

for word in inputSet:

if word in vocabList:

returnVec[vocabList.index(word)] += 1

return returnVec

def countX(aList,el):

count = 0

for item in aList:

if item == el:

count += 1

return count

def trainNB0(trainMatrix,trainCategory):

'''

trainMatrix:文檔矩陣

trainCategory:每篇文檔類別標(biāo)簽

'''

numTrainDocs = len(trainMatrix)

numWords = len(trainMatrix[0])

pAbusive0 = countX(trainCategory,0) / float(numTrainDocs)

pAbusive1 = countX(trainCategory,1) / float(numTrainDocs)

pAbusive2 = countX(trainCategory,2) / float(numTrainDocs)

pAbusive3 = countX(trainCategory,3) / float(numTrainDocs)

pAbusive4 = countX(trainCategory,4) / float(numTrainDocs)

#初始化所有詞出現(xiàn)數(shù)為1，并將分母初始化為2，避免某一個概率值為0

p0Num = ones(numWords); p1Num = ones(numWords)

p2Num = ones(numWords)

p3Num = ones(numWords)

p4Num = ones(numWords)

p0Denom = 2.0; p1Denom = 2.0 ;p2Denom = 2.0

p3Denom = 2.0; p4Denom = 2.0

for i in range(numTrainDocs):

# 1類的矩陣相加

if trainCategory[i] == 1:

p1Num += trainMatrix[i]

p1Denom += sum(trainMatrix[i])

if trainCategory[i] == 2:

p2Num += trainMatrix[i]

p2Denom += sum(trainMatrix[i])

if trainCategory[i] == 3:

p3Num += trainMatrix[i]

p3Denom += sum(trainMatrix[i])

if trainCategory[i] == 4:

p4Num += trainMatrix[i]

p4Denom += sum(trainMatrix[i])

if trainCategory[i] == 0:

p0Num += trainMatrix[i]

p0Denom += sum(trainMatrix[i])

#將結(jié)果取自然對數(shù)，避免下溢出，即太多很小的數(shù)相乘造成的影響

p4Vect = log(p4Num/p4Denom)

p3Vect = log(p3Num/p3Denom)

p2Vect = log(p2Num/p2Denom)

p1Vect = log(p1Num/p1Denom)#change to log()

p0Vect = log(p0Num/p0Denom)#change to log()

return p0Vect,p1Vect,p2Vect,p3Vect,p4Vect,pAbusive0,pAbusive1,pAbusive2,pAbusive3,pAbusive4

def classifyNB(vec2Classify,p0Vec,p1Vec,p2Vec,p3Vec,p4Vec,pClass0,pClass1,pClass2,pClass3,pClass4):

p1 = sum(vec2Classify * p1Vec) + log(pClass1)

p2 = sum(vec2Classify * p2Vec) + log(pClass2)

p3 = sum(vec2Classify * p3Vec) + log(pClass3)

p4 = sum(vec2Classify * p4Vec) + log(pClass4)

p0 = sum(vec2Classify * p0Vec) + log(pClass0)

## print(p0,p1,p2,p3,p4)無錫人流醫(yī)院 http://www.bhnkyy39.com/

return [p0,p1,p2,p3,p4].index(max([p0,p1,p2,p3,p4]))

if __name__ == "__main__":

dataset = [['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'],

['i','love','you'],

['you','kiss','me'],

['hate','heng','no'],

['can','i','hug','you'],

['refuse','me','ache'],

['1','4','3'],

['5','2','3'],

['1','2','3']]

# 0，1，2，3，4分別表示不同類別

classVec = [0,1,0,1,0,1,2,2,4,2,4,3,3,3]

print("正在創(chuàng)建詞頻列表")

myVocabList = createVocabList(dataset)

print("正在建詞向量")

trainMat = []

for postinDoc in dataset:

trainMat.append(setOfWords2Vec(myVocabList,postinDoc))

print("開始訓(xùn)練")

p0V,p1V,p2V,p3V,p4V,pAb0,pAb1,pAb2,pAb3,pAb4 = trainNB0(array(trainMat),array(classVec))

# 輸入的測試案例

tmp = ['love','you','kiss','you']

thisDoc = array(setOfWords2Vec(myVocabList,tmp))

flag = classifyNB(thisDoc,p0V,p1V,p2V,p3V,p4V,pAb0,pAb1,pAb2,pAb3,pAb4)

print('flag is',flag)