The Mystery of the PROC SORT Options NODUPRECS and

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1、SUGI30Coders'CornerPaper037-30TheMysteryofthePROCSORTOptionsNODUPRECSandNODUPKEYRevealedBrittaKelsey,MGIPharma,Inc.,Bloomington,MNABSTRACTTheNODUPRECS(orNODUP)andNODUPKEYoptionscanbeusefulwiththeSORTprocedurebuttheycanbedangerousifyoudonotunderstandthemcompletely

2、.Theyworksimilarlyinthattheybothcaneliminateunwantedobservations,butNODUPRECScomparesallthevariablesinyourdatasetwhileNODUPKEYcomparesjusttheBYvariables.Also,youmustbeawareofhowyourdatasetiscurrentlysortedtoeliminatetheobservationsthatyouwantbecausetheseoptionsco

3、mpareadjacentobservations.Inthispaper,IwilldescribethisingreaterdetailandshowexamplesofhowtousetheNODUPRECSandNODUPKEYoptions.AllexamplesshownweredoneintheSAS®systemforPCs,version8.2.TheintendedaudienceforthispaperisbeginnerlevelSASprogrammers.INTRODUCTIONTherese

4、emstobeconfusionamongSASusersabouttheNODUPRECS(orNODUP)andNODUPKEYoptions.Thesecanbeveryusefulbutdangerousifyouarenotclearonhowtheywork.IwillbringsomeclarificationtothesePROCSORToptionsandwillshowsomeexamplesofhowtheyworksoyoucanputthemtogooduse.Throughouttherest

5、ofthispaperIwillbeusingthealiasNODUPfortheNODUPRECSoption.DEFININGNODUPANDNODUPKEYOPTIONSTheNODUPoptionchecksforandeliminatesduplicateobservations.Ifyouspecifythisoption,PROCSORTcomparesallvariablevaluesforeachobservationtothoseforthepreviousobservationthatwaswri

6、ttentotheoutputdataset.Ifanexactmatchisfound,theobservationisnotwrittentotheoutputdataset.TheNODUPKEYoptionchecksforandeliminatesobservationswithduplicateBYvariablevalues.Ifyouspecifythisoption,PROCSORTcomparesallBYvariablevaluesforeachobservationtothoseforthepre

7、viousobservationwrittentotheoutputdataset.IfanexactmatchusingtheBYvariablevaluesisfound,theobservationisnotwrittentotheoutputdataset.NoticethatwiththeNODUPKEYoption,PROCSORTiscomparingallBYvariablevalueswhiletheNODUPoptioncomparesallthevariablesinthedatasetthatis

8、beingsorted.Aneasywaytorememberthedifferencebetweentheseoptionsistokeepinmindtheword“key”inNODUPKEY.Itevaluatesthe“key”orBYvariablevaluesthatyouspecify.Onethin