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1、2Import/ExportDataThemaingoalsofthischapteraretofamiliarizeyouwiththevariousclassesofobjectsinR,helpthereaderextractdatafromvariouspopularformats,connectRwithpopulardatabasessuchasMySQL,andfinallythebestexportoptionsoftheRoutput.Themainpurposeisthatthepractitionerfrequentlyhasdataavail
2、ableinafixedformat,andsometimesthedatasetisavailableinpopulardatabasesystems.Thischapterhelpsyoutoextractthedatafromvarioussources,andthenalsorecommendsthebestexportoptionsoftheRoutput.WewillthoughbeginwithabetterunderstandingofthevariousformatsinwhichRstoresthedata.Updatedinformationa
3、bouttheimport/exportoptionsismaintainedathttp://cran.r-project.org/doc/manuals/R-data.html.Tosummarize,themainlearningfromthischapterwouldbethefollowing:BasicandessentialcomputationsinRImportingdatafromCSV,XLS,andfewmoreExportingdataforothersoftwareRsessionmanagementdata.frameandotherf
4、ormatsAnysoftwarecomeswithitsstructureandnuances.TheQuestionnaireanditscomponentsectionofChapter1,DataCharacteristics,introducedvariousfacetsofdata.InthecurrentsectionwewillgointothedetailsofhowRworkswithdataofdifferentcharacteristics.Dependingontheneedwehavedifferentformatsofthedata.I
5、nthissection,wewillbeginwithsimplerobjectsandmoveuptheladdertowardssomeofthemorecomplexones.Import/ExportDataConstants,vectors,andmatricesRhasfiveinbuiltobjectswhichstorecertainconstantvalues.ThefiveobjectsareLETTERS,letters,month.abb,month.name,andpi.Thefirsttwoobjectscontaintheletter
6、sA-Zinupperandlowercases.Thethirdandfourthobjectshavemonth'sabbreviatedformandthecompletemonthnames.Finally,theobjectpicontainsthevalueofthefamousirrationalnumber.So,theexercisehereisforyoutofindthevalueoftheirrationalnumbere.ThedetailsabouttheseRconstantobjectsmaybeobtainedusingthefun
7、ction?Constantsorexample(Constants),ofcoursebyexecutingthesecommandsintheconsole.ThereisalsoanotherclassofconstantsinRwhichisveryuseful.TheseconstantsarecalledNumericConstantsandincludeInfforinfinitenumbers,NaNfornotanumber,andsoon.Youareencouragedtofindmoredetailsandotherusefulconst
