吴裕雄 python 机器学习-DMT（1）
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import
numpy as np
import
operator as op
from math import log
def createDataSet():
dataSet = [[1, 1, ‘yes‘],
[1, 1, ‘yes‘],
[1, 0, ‘no‘],
[0, 1, ‘no‘],
[0, 1, ‘no‘]]
labels = [‘no surfacing‘,‘flippers‘]
return dataSet, labels
dataSet,labels = createDataSet()
print(dataSet)
print(labels)
def calcShannonEnt(dataSet):
labelCounts = {}
for featVec in dataSet:
currentLabel = featVec[-1]
if(currentLabel notin labelCounts.keys()):
labelCounts[currentLabel] = 0
labelCounts[currentLabel] += 1
shannonEnt = 0.0
rowNum = len(dataSet)
for key in labelCounts:
prob = float(labelCounts[key])/rowNum
shannonEnt -= prob * log(prob,2)
return shannonEnt
shannonEnt = calcShannonEnt(dataSet)
print(shannonEnt)
def splitDataSet(dataSet, axis, value):
retDataSet = []
for featVec in dataSet:
if(featVec[axis] == value):
reducedFeatVec = featVec[:axis]
reducedFeatVec.extend(featVec[axis+1:])
retDataSet.append(reducedFeatVec)
return retDataSet
retDataSet = splitDataSet(dataSet,1,1)
print(np.array(retDataSet))
retDataSet = splitDataSet(dataSet,1,0)
print(retDataSet)
def chooseBestFeatureToSplit(dataSet):
numFeatures = np.shape(dataSet)[1]-1
baseEntropy = calcShannonEnt(dataSet)
bestInfoGain = 0.0
bestFeature = -1
for i in range(numFeatures):
featList = [example[i] for example in dataSet]
uniqueVals = set(featList)
newEntropy = 0.0
for value in uniqueVals:
subDataSet = splitDataSet(dataSet, i, value)
prob = len(subDataSet)/float(len(dataSet))
newEntropy += prob * calcShannonEnt(subDataSet)
infoGain = baseEntropy - newEntropy
if (infoGain > bestInfoGain):
bestInfoGain = infoGain
bestFeature = i
return bestFeature
bestFeature = chooseBestFeatureToSplit(dataSet)
print(bestFeature)
def majorityCnt(classList):
classCount={}
for vote in classList:
if(vote notin classCount.keys()):
classCount[vote] = 0
classCount[vote] += 1
sortedClassCount = sorted(classCount.items(), key=op.itemgetter(1), reverse=True)
return sortedClassCount[0][0]
def createTree(dataSet,labels):
classList = [example[-1] for example in dataSet]
if(classList.count(classList[0]) == len(classList)):
return classList[0]
if len(dataSet[0]) == 1:
return majorityCnt(classList)
bestFeat = chooseBestFeatureToSplit(dataSet)
bestFeatLabel = labels[bestFeat]
myTree = {bestFeatLabel:{}}
del(labels[bestFeat])
featValues = [example[bestFeat] for example in dataSet]
uniqueVals = set(featValues)
for value in uniqueVals:
subLabels = labels[:]
myTree[bestFeatLabel][value] = createTree(splitDataSet(dataSet, bestFeat, value),subLabels)
return myTree
myTree = createTree(dataSet,labels)
print(myTree)
def classify(inputTree,featLabels,testVec):
for i in inputTree.keys():
firstStr = i
break
secondDict = inputTree[firstStr]
featIndex = featLabels.index(firstStr)
key = testVec[featIndex]
valueOfFeat = secondDict[key]
if isinstance(valueOfFeat, dict):
classLabel = classify(valueOfFeat, featLabels, testVec)
else:
classLabel = valueOfFeat
return classLabel
featLabels = [‘no surfacing‘, ‘flippers‘]
classLabel = classify(myTree,featLabels,[1,1])
print(classLabel)
import pickle
def storeTree(inputTree,filename):
fw = open(filename,‘wb‘)
pickle.dump(inputTree,fw)
fw.close()
def grabTree(filename):
fr = open(filename,‘rb‘)
return pickle.load(fr)
filename = "D:\\mytree.txt"
storeTree(myTree,filename)
mySecTree = grabTree(filename)
print(mySecTree)
featLabels = [‘no surfacing‘, ‘flippers‘]
classLabel = classify(mySecTree,featLabels,[0,0])
print(classLabel)
原文：https://www.cnblogs.com/tszr/p/10148597.html
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