机器学习实战：第九章 树回归

Posted 2020-10-10 黑凤梨

源代码中有两处错误，在网上查找后解决。

 

from numpy import *
import matplotlib.pyplot as plt

def loadDataSet(fileName):
    dataSet = []
    fr=open(fileName)
    for line in fr.readlines():
        curLine = line.strip().split(‘\t‘)
        fltLine=map(float,curLine)
        dataSet.append(list(fltLine))
    return dataSet


def binSplitDataSet(dataSet, feature, value):
    mat0 = dataSet[nonzero(dataSet[:,feature] > value)[0],:]     ##  第一处错误
    mat1 = dataSet[nonzero(dataSet[:,feature] <= value)[0],:]
    return mat0,mat1


def regLeaf(dataSet):#returns the value used for each leaf
    return mean(dataSet[:, -1])


def regErr(dataSet):
    return var(dataSet[:,-1]) * shape(dataSet)[0]

def chooseBestSplit(dataSet, leafType=regLeaf, errType=regErr, ops=(1,4)):
    tolS = ops[0]
    tolN = ops[1]
    #if all the target variables are the same value: quit and return value
    if len(set(dataSet[:, -1].T.tolist()[0])) == 1: #exit cond 1
        return None , leafType(dataSet)
    m,n = shape(dataSet)
    #the choice of the best feature is driven by Reduction in RSS error from mean
    S = errType(dataSet)
    bestS = inf; bestIndex = 0; bestValue = 0
    for featIndex in range(n-1):
        #for splitVal in set(dataSet[:,featIndex]):

        ## 第二处错误
        for splitVal in set((dataSet[:, featIndex].T.tolist())[0]):                        
            mat0, mat1 = binSplitDataSet(dataSet, featIndex, splitVal)
            if (shape(mat0)[0] < tolN) or (shape(mat1)[0] < tolN): continue
            newS = errType(mat0) + errType(mat1)
            if newS < bestS:
                bestIndex = featIndex
                bestValue = splitVal
                bestS = newS
    #if the decrease (S-bestS) is less than a threshold don‘t do the split
    if (S - bestS) < tolS:
        return None, leafType(dataSet) #exit cond 2
    mat0, mat1 = binSplitDataSet(dataSet, bestIndex, bestValue)
    if (shape(mat0)[0] < tolN) or (shape(mat1)[0] < tolN):  #exit cond 3
        return None, leafType(dataSet)
    return bestIndex,bestValue#returns the best feature to split on
                              #and the value used for that split


def createTree(dataSet, leafType=regLeaf, errType=regErr, ops=(1,4)):#assume dataSet is NumPy Mat so we can array filtering
    feat, val = chooseBestSplit(dataSet, leafType, errType, ops)#choose the best split
    if feat == None: return val #if the splitting hit a stop condition return val
    retTree = {}
    retTree[‘spInd‘] = feat
    retTree[‘spVal‘] = val
    lSet, rSet = binSplitDataSet(dataSet, feat, val)
    retTree[‘left‘] = createTree(lSet, leafType, errType, ops)
    retTree[‘right‘] = createTree(rSet, leafType, errType, ops)
    return retTree

###########################################
#  example construct a simple regression tree
myDat1 = loadDataSet(r‘train.txt‘)
myMat = mat(myDat1)
mytree = createTree(myMat)
mytree=createTree(myMat,ops=(1,4))
print(mytree)
x=[];y=[]
for a in myDat1:
    x.append(a[:][-2])
    y.append(a[:][-1])
plt.scatter(x,y)
plt.show()
#############################
# cut some branches
def isTree(obj):
    return (type(obj).__name__==‘dict‘)

def getMean(tree):
    if isTree(tree[‘right‘]): tree[‘right‘] = getMean(tree[‘right‘])
    if isTree(tree[‘left‘]): tree[‘left‘] = getMean(tree[‘left‘])
    return (tree[‘left‘]+tree[‘right‘])/2.0

def prune(tree, testData):
    if shape(testData)[0] == 0: return getMean(tree) #if we have no test data collapse the tree
    if (isTree(tree[‘right‘]) or isTree(tree[‘left‘])):#if the branches are not trees try to prune them
        lSet, rSet = binSplitDataSet(testData, tree[‘spInd‘], tree[‘spVal‘])
    if isTree(tree[‘left‘]): tree[‘left‘] = prune(tree[‘left‘], lSet)
    if isTree(tree[‘right‘]): tree[‘right‘] =  prune(tree[‘right‘], rSet)
    #if they are now both leafs, see if we can merge them
    if not isTree(tree[‘left‘]) and not isTree(tree[‘right‘]):
        lSet, rSet = binSplitDataSet(testData, tree[‘spInd‘], tree[‘spVal‘])
        errorNoMerge = sum(power(lSet[:,-1] - tree[‘left‘],2)) +            sum(power(rSet[:,-1] - tree[‘right‘],2))
        treeMean = (tree[‘left‘]+tree[‘right‘])/2.0
        errorMerge = sum(power(testData[:,-1] - treeMean,2))
        if errorMerge < errorNoMerge:
            print ("merging")
            return treeMean
        else: return tree
    else: return tree

mydatTest=loadDataSet(‘test.txt‘)
mymatTest=mat(mydatTest)
cut_tree=prune(mytree,mymatTest)
print(cut_tree)

################################
#model tree

def linearSolve(dataSet):   #helper function used in two places
    m,n = shape(dataSet)
    X = mat(ones((m,n))); Y = mat(ones((m,1)))#create a copy of data with 1 in 0th postion
    X[:,1:n] = dataSet[:,0:n-1]; Y = dataSet[:,-1]#and strip out Y
    xTx = X.T*X
    if linalg.det(xTx) == 0.0:
        raise NameError(‘This matrix is singular, cannot do inverse,\n        try increasing the second value of ops‘)
    ws = xTx.I * (X.T * Y)
    return ws,X,Y

def modelLeaf(dataSet):
    ws,X,Y =linearSolve(dataSet)
    return ws

def modelErr(dataSet):
    ws,X,Y = linearSolve(dataSet)
    yHat = X* ws
    return sum(power(Y - yHat,2))

def regTreeEval(model, inDat):
    return float(model)

def modelTreeEval(model, inDat):
    n = shape(inDat)[1]
    X = mat(ones((1,n+1)))
    X[:,1:n+1]=inDat
    return float(X*model)

def treeForeCast(tree, inData, modelEval=regTreeEval):
    if not isTree(tree): return modelEval(tree, inData)
    if inData[tree[‘spInd‘]] > tree[‘spVal‘]:
        if isTree(tree[‘left‘]):
            return treeForeCast(tree[‘left‘], inData, modelEval)
        else:
            return modelEval(tree[‘left‘], inData)
    else:
        if isTree(tree[‘right‘]):
            return treeForeCast(tree[‘right‘], inData, modelEval)
        else:
            return modelEval(tree[‘right‘], inData)

def createForeCast(tree, testData, modelEval=regTreeEval):
    m = len(testData)
    yHat = mat(zeros((m, 1)))
    for i in range(m):
        yHat[i, 0] = treeForeCast(tree, mat(testData[i]), modelEval)
    return yHat

trainmat=mat(loadDataSet(‘train.txt‘))
testdat=loadDataSet(‘test.txt‘)
testmat=mat(testdat)
print(testmat[:,1])

mytree=createTree(trainmat,ops=(1,4))
yHat=createForeCast(mytree,testmat[:,0])
#print(yHat)
co1=corrcoef(yHat,testmat[:,1],rowvar=0)[0,1]
print(co1)

#mytree=createTree(trainmat,modelLeaf,modelErr,(0,20))
#yHat=createForeCast(mytree,testmat[:,0],modelTreeEval)
#co2=corrcoef(yHat,testmat[:,1],rowvar=0)[0,1]
#print(co2)