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1、The Little SAS Book: A Primer, Fifth EditionChapter3:WorkingWithYourData"Contrariwise,"continuedTweedledee,"ifitwasso,itmightbe;andifitwereso,itwouldbe;butasitisn't,itain't.That'slogic."LewisCarrollFromAliceThroughtheLookingGlassbyLewisCarroll.Publicdomain.3.1Cre
2、atingandRedefiningVariablesIfsomeoneweretocompilealistofthemostpopularthingstodowithSASsoftware,creatingandredefiningvariableswouldsurelybenearthetop.Fortunately,SASisflexibleandusesacommonsenseapproachtothesetasks.Youcreateandredefinevariableswithassignmentstate
3、mentsusingthisbasicform:variable=expression;Ontheleftsideoftheequalsignisavariablename,eitherneworold.Ontherightsideoftheequalsignmayappearaconstant,anothervariable,oramathematicalexpression.Hereareexamplesofthesebasictypesofassignmentstatements:TypeofexpressionA
4、ssignmentstatementnumericconstantQwerty=10;characterconstantQwerty='ten';avariableQwerty=OldVar;additionQwerty=OldVar+10;subtractionQwerty=OldVar-10;multiplicationQwerty=OldVar*10;divisionQwerty=OldVar/10;exponentiationQwerty=OldVar**10;WhetherthevariableQwertyis
5、numericorcharacterdependsontheexpressionthatdefinesit.Whentheexpressionisnumeric,Qwertywillbenumeric;whenitischaracter,Qwertywillbecharacter.Whendecidinghowtointerpretyourexpression,SASfollowsthestandardmathematicalrulesofprecedence:SASperformsexponentiationfirst
6、,thenmultiplicationanddivision,followedbyadditionandsubtraction.Youcanuseparenthesestooverridethatorder.HerearetwosimilarSASstatementsshowingthatacoupleofparenthesescanmakeabigdifference:AssignmentstatementResultx=10*4+3**2;x=49x=10*(4+3**2);x=130WhileSAScanreade
7、xpressionswithorwithoutparentheses,peopleoftencan't.Ifyouuseparentheses,yourprogramswillbealoteasiertoread.ExampleThefollowingrawdataarefromasurveyofhomegardeners.Gardenerswereaskedtoestimatethenumberofpoundstheyharvestedforfourcrops:tomatoes,zucchini,peas,andgra
8、pes.Gregor102400Molly155101000Luther50101550Susan200.20ThisprogramreadsthedatafromafilecalledGarden.dat,andthenmodifiesthedata:Page2/21SAS Institute, SAS Insti
