资源描述：
《cluster analysis》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。
1、9ClusteranalysisClustering,alsoknownassegmentation,whichIwilldescribemorefullybelow,isthemostwidespreaddescriptivemethodofdataanalysisanddatamining.Itisusedwhenthereisalargevolumeofdataandtheaimistofindhomogeneoussubsets,whichcanbeprocessedandanalysedindifferentways.Sucharequirementispresentinaw
2、iderangeofcontexts,especiallyinthesocialsciences,medicineandmarketing,wherehumanfactorsmeanthatthedataarenumerousanddifficulttounderstand.Inclustering,unlikeclassification(whichwillbedealtwithinalaterchapter),thereisnoparticulardependentvariable,anditishardertocomparetwoformsofclusteringobjective
3、ly.Thereisnoprivilegedcriterionforcomparingtwoalgorithms,suchaswefindintherateofcorrectclassification,andmanycompetingalgorithmsvieforourattention.Onlythemainoneswillbedescribedhere,butitisworthnotingthatthetheoryisconstantlyandrapidlyevolvinginthisfield,especiallynowthattextminingandwebminingareb
4、eginningtogiverisetoproblemsofdocumentclustering.9.1DefinitionofclusteringClusteringisthestatisticaloperationofgroupingobjects(individualsorvariables)intoalimitednumberofgroupsknownasclusters(orsegments),whichhavetwoproperties.Ontheonehand,theyarenotdefinedinadvancebytheanalyst,butarediscovereddu
5、ringtheoperation,unliketheclassesusedinclassification.Ontheotherhand,theclustersarecombinationsofobjectshavingsimilarcharacteristics,whichareseparatedfromobjectshavingdifferentcharacteristics(resultingininternalhomogeneityandexternalheteroge-neity).Thiscanbemeasuredbycriteriasuchasthebetween-clu
6、stersumofsquares(seebelow).Aswithclassification,theessenceofclusteringisthedistributionofobjectsintogroups.However,thisdistributionisnotcarriedoutonthebasisofapredefinedcriterion,andisnotintendedtocombinetheobjectshavingthesamevalueforsuchacriterion.Inotherwords,theclustertowhicheachobjectbelongs
7、isnotknowninadvance,incontrasttotheclassificationprocess.Eventhenumberofclustersisnotalwaysfixedinadvance.ThisisbecausethereisnoDataMiningandStatisticsforDecisionMaking,FirstEdition.Ste´phaneTuffe´ry.Ó2011JohnWiley&Sons,Ltd.Publishe
