Apriori算法
2016-07-20 09:03
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假如有4条记录
[[1, 3, 4], [2, 3, 5], [1, 2, 3, 5], [2, 5]]
那么集合{1}的支持度为2/4,即出现记次数/总记录数。
一条规则P-H的可信度为 support(P&&H)/support(P)
机器学习实战的算法首先枚举了所有计算出来满足支持度的记录,然后以枚举的为P&&H,然后再枚举子集,用P&&H/(P&&H-子集)计算可信度。
[[1, 3, 4], [2, 3, 5], [1, 2, 3, 5], [2, 5]]
那么集合{1}的支持度为2/4,即出现记次数/总记录数。
一条规则P-H的可信度为 support(P&&H)/support(P)
机器学习实战的算法首先枚举了所有计算出来满足支持度的记录,然后以枚举的为P&&H,然后再枚举子集,用P&&H/(P&&H-子集)计算可信度。
from numpy import * def loadDataSet(): return [[1, 3, 4], [2, 3, 5], [1, 2, 3, 5], [2, 5]] def createC1(dataSet): C1 = [] for transaction in dataSet: for item in transaction: if not [item] in C1: C1.append([item]) C1.sort() return map(frozenset, C1) def scanD(D, Ck, minSupport): ssCnt = {} for tid in D: for can in Ck: if can.issubset(tid): if not ssCnt.has_key(can): ssCnt[can]=1 else: ssCnt[can] += 1 numItems = float(len(D)) retList = [] supportData = {} for key in ssCnt: support = ssCnt[key]/numItems if support >= minSupport: retList.insert(0,key) supportData[key] = support return retList, supportData def aprioriGen(Lk, k): retList = [] lenLk = len(Lk) for i in range(lenLk): for j in range(i+1, lenLk): L1 = list(Lk[i])[:k-2]; L2 = list(Lk[j])[:k-2] L1.sort(); L2.sort() if L1==L2: retList.append(Lk[i] | Lk[j]) return retList def apriori(dataSet, minSupport = 0.5): C1 = createC1(dataSet) D = map(set, dataSet) L1, supportData = scanD(D, C1, minSupport) L = [L1] k = 2 while (len(L[k-2]) > 0): Ck = aprioriGen(L[k-2], k) Lk, supK = scanD(D, Ck, minSupport) supportData.update(supK) L.append(Lk) k += 1 return L, supportData def generateRules(L, supportData, minConf=0.7): bigRuleList = [] for i in range(1, len(L)): for freqSet in L[i]: H1 = [frozenset([item]) for item in freqSet] print(H1) if (i > 1): rulesFromConseq(freqSet, H1, supportData, bigRuleList, minConf) else: calcConf(freqSet, H1, supportData, bigRuleList, minConf) return bigRuleList def calcConf(freqSet, H, supportData, brl, minConf=0.7): prunedH = [] for conseq in H: conf = supportData[freqSet]/supportData[freqSet-conseq] if conf >= minConf: print freqSet-conseq,'-->',conseq,'conf:',conf brl.append((freqSet-conseq, conseq, conf)) prunedH.append(conseq) return prunedH def rulesFromConseq(freqSet, H, supportData, brl, minConf=0.7): m = len(H[0]) if (len(freqSet) > (m + 1)): Hmp1 = aprioriGen(H, m+1) Hmp1 = calcConf(freqSet, Hmp1, supportData, brl, minConf) if (len(Hmp1) > 1): rulesFromConseq(freqSet, Hmp1, supportData, brl, minConf) def pntRules(ruleList, itemMeaning): for ruleTup in ruleList: for item in ruleTup[0]: print itemMeaning[item] print " -------->" for item in ruleTup[1]: print itemMeaning[item] print "confidence: %f" % ruleTup[2] print
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