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1、SUGI30TutorialsPaper247-30TheBasicsofUsingSAS?IndexesMichaelA.Raithel,Westat,Rockville,MDAbstractIftherewasaSASperformancetoolthatcoulddrasticallyreduceyourprogram’sI/O’sandresponsetime,andloweritsCPUtime,wouldyouuseit?Well,thistypeofperformancetoolexists;itiscalled“SASInd
2、exes.”SASIndexescandramaticallyimprovetheperformanceofprogramsthataccesssmallsubsetsofobservationsfromlargeSASdatasets.However,manySASprogrammersneverbothertolearnaboutthemortousethem.ThisisyouropportunitytoaddthisperformancetooltoyourSASprogrammingrepertoire.Thispaperdisc
3、usseshowtocreatesimpleandcompositeSASindexes,howtodeterminewhichvariablesmakegoodindexkeyvariables,whencreatingandusingindexesisappropriate,whatcentilesare,andhowtogenerateindexusagemessages.Itillustrateshowindexescanimproveprocessingwhensubsettingand/orupdatingalargeSASda
4、tasetandwhenanindexcanoptimizeaBYstatement.Afterreadingthispaper,youwillhavethebasicinformationthatyouneedtocreateanduseSASIndexestoimprovetheperformanceofyourSASapplications.IntroductionItisnottoohardtounderstandhowaSASindexcanhelpyoutodirectlyaccesstheobservationsthatyou
5、needinaparticularSASdataset.Asanexercise,dothefollowing:OpenSASOnlineDocumentation,ClickontheSearchtab,entertheword“rtrace”intotheSearchtab’swindow,andclickon.TheSASOnlineDocumentationsearchfunctionwillreturnaboutadozenlinks.Whenyouclickonanyofthoselinks,yougodirec
6、tlytoapageinthedocumentationthatdiscussestheSASRTRACEfacility.ThissavesyouthetediouseffortofgoingthroughtheentireSASOnlinedocumentation,page-by-page,lookingforoccurrencesoftheword“rtrace”.ASASindexisanalogoustothesearchfunction,above.Agoodindexwillallowyourprogramstoquickl
7、yaccessthesubsetofSASobservationsthatyouneedfromalargeSASdataset.ThiswilldramaticallyimprovethespeedandefficiencyofyourSASprograms.Conversely,abadlyconceivedSASindexwillreturnfartoomanyobservationsandbenobetterthanreadingtheentiredatasetsequentially.(Inkeepingwiththeanalog
8、y,above,considerhowmanypageswouldbereturnedandhowmuchlongeritwouldtakeifyousearchedtheSAS
