The Basics of Using SAS Indexes

The Basics of Using SAS Indexes

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时间:2019-07-16

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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

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