KNN-近邻算法主要思路:给出一个向量inX,将dataSet的每一个点距离该点的距离d求出,根据d排序,得序号下标,而每个点(一行)对应一个label(通常为最后一个属性),顺序取得前k个d,并将其相同label计数,将label按数量递减排序,取最多数量的label输出
思路:给出一个向量inX,将dataSet的每一个点距离该点的距离d求出,根据d排序,得序号下标,而每个点(一行)对应一个label(通常为最后一个属性),顺序取得前k个d,并将其相同label计数,将label按数量递减排序,取最多数量的label输出 def classify0(inX, dataSet, labels, k): dataSetSize = dataSet.shape[0] diffMat = tile(inX, (dataSetSize,1)) - dataSet sqDiffMat = diffMat**2 sqDistances = sqDiffMat.sum(axis=1) distances = sqDistances**0.5 sortedDistIndicies = distances.argsort() classCount={} for i in range(k): voteIlabel = labels[sortedDistIndicies[i]] classCount[voteIlabel] = classCount.get(voteIlabel,0) + 1 sortedClassCount = sorted(classCount.items(), key=operator.itemgetter(1), reverse=True) return sortedClassCount[0][0] 思路:读取数据,数据必须和代码放在一起,否则需要写完整的路径。注意:returnMat[index,:]i执行一次,读取fr的一行的前三个属性,最后构成读取fr数据的前三列;classLabelVector每次执行一次,读取fr的一行的最后一个属性构成读取fr数据的最后一列的值,构成一个list def file2matrix(filename): fr = open(filename) numberOfLines = len(fr.readlines()) #get the number of lines in the file returnMat = zeros((numberOfLines,3)) #prepare matrix to return classLabelVector = [] #prepare labels return fr = open(filename) index = 0 for line in fr.readlines(): line = line.strip() listFromLine = line.split('\t') returnMat[index,:] = listFromLine[0:3] classLabelVector.append(int(listFromLine[-1])) index += 1 return returnMat,classLabelVector 思路:数值归一化就是将取值范围处理为0-1或者-1-1之间, 公式:newValue=(oldValue-min)/(max-min)注意dataSet.min(0)可以取得列最小的值 def autoNorm(dataSet): minVals = dataSet.min(0) maxVals = dataSet.max(0) ranges = maxVals - minVals normDataSet = zeros(shape(dataSet)) m = dataSet.shape[0] normDataSet = dataSet - tile(minVals, (m,1)) normDataSet = normDataSet/tile(ranges, (m,1)) #element wise divide return normDataSet, ranges, minVals 思路:取datingTestSet2.txt的前50%,每一行作为inX测试向量,取datingTestSet2.txt的后50%作为训练集,此时的label是datingTestSet2.txt的后50%的最后一列,k=3。每次预测的值和datingTestSet2.txt相对应的行的最后一列(实例)比对,如果不对,计数+1,输出错误率=错误数/测试集 def datingClassTest(): hoRatio = 0.50 #hold out 50% datingDataMat,datingLabels = file2matrix('datingTestSet2.txt') #load data setfrom file normMat, ranges, minVals = autoNorm(datingDataMat) m = normMat.shape[0] numTestVecs = int(m*hoRatio) errorCount = 0.0 for i in range(numTestVecs): classifierResult = classify0(normMat[i,:],normMat[numTestVecs:m,:],datingLabels[numTestVecs:m],3) print ("the classifier came back with: %d, the real answer is: %d" % (classifierResult, datingLabels[i])) if (classifierResult != datingLabels[i]): errorCount += 1.0 print ("the total error rate is: %f" % (errorCount/float(numTestVecs))) print (errorCount)