TheStataJournal20077Number2pp268271Statatip45GettingthosedataintoshapeChristopherFBaumDepartmentofEconomicsBostonCollegeChestnutHillMA02467baumbceduNicholasJCoxDepartmentofGeographyDurhamU ID: 415792
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TheStataJournalEditorJosephNewtonDepartmentofStatisticsTexasA&MUniversityCollegeStation,Texas77843979-845-3142;FAX979-845-3144jnewton@stata-journal.comEditorNicholasJ.CoxDepartmentofGeographyDurhamUniversitySouthRoadDurhamCityDH13LEUKn.j.cox@stata-journal.comAssociateEditorsChristopherF.BaumBostonCollegeRinoBellocco TheStataJournal(2007)7,Number2,pp.268{271Statatip45:GettingthosedataintoshapeChristopherF.BaumDepartmentofEconomicsBostonCollegeChestnutHill,MA02467baum@bc.eduNicholasJ.CoxDepartmentofGeographyDurhamUniversityDurhamCity,UKn.j.cox@durham.ac.ukAreyourdatainshape?Thatis,aretheyinthestructurethatyouneedtoconducttheanalysisyouhaveinmind?Datasourcesoftenprovidethedatainastructurethatissuitableforpresentationbutclumsyforstatisticalanalysis.OneofthekeydatamanagementtoolsthatStataprovidesisreshape;see[D]reshape.Ifyouneedtomodifythestructureofyourdata,youshouldbefamiliarwithreshapeanditstwofunctions:reshapewideandreshapelong.Inthistip,wediscusshowtwoapplicationsofreshapemaybethesolutiontosomeknottydatamanagementproblems.Asa rstexample,considerthisquestionpostedonStatalistbyanindividualwhohasadatasetinthewideform:countrytradeflowYr1990Yr1991Armeniaimports105120Armeniaexports90100Boliviaimports200230Boliviaexports80115Colombiaimports100105Colombiaexports7071Hewouldliketoreshapethedataintolongform:countryyearimportsexportsArmenia199010590Armenia1991120100Bolivia199020080Bolivia1991230115Colombia199010070Colombia199110571c\r2007StataCorpLPdm0031 C.F.BaumandN.J.Cox269Wemustexchangetherolesofyearsandtrade\rowsintheoriginaldatatoarriveatthedesiredstructure,suitableforanalysisasxtdata.Thisexchangecanbehandledbytwosuccessiveapplicationsofreshape:.reshapelongYr,i(countrytradeflow)(note:j=19901991)Datawide�-longNumberofobs.6�-12Numberofvariables4�-4jvariable(2values)�-_jxijvariables:Yr1990Yr1991�-YrThistransformationswingsthedataintolongformwitheachobservationidenti edbycountry,tradeflow,andthenewvariablej,takingonthevaluesofyear.Wenowperformreshapewidetomakeimportsandexportsintoseparatevariables:.rename_jyear.reshapewideYr,i(countryyear)j(tradeflow)string(note:j=exportsimports)Datalong�-wideNumberofobs.12�-6Numberofvariables4�-4jvariable(2values)tradeflow�-(dropped)xijvariables:Yr�-YrexportsYrimportsIfwetransformthedatatowideformonceagain,thei()optioncontainscountryandyear,asthosearethedesiredidenti ersoneachobservationofthetargetdataset.Wespecifythattradeflowisthej()variableforreshape,indicatingthatitisastringvariable.Thedatanowhavethedesiredstructure.Althoughwehaveillustratedthisdouble-reshapetransformationwithonlyafewcountries,years,andvariables,thetechniquegeneralizestoanynumberofeach.Asasecondexampleofsuccessiveapplicationsofreshape,considertheWorldBank'sWorldDevelopmentIndicators(WDI)dataset.1Theirextractprogramgen-eratesacomma-separatedvalue(CSV)databaseextract,readablebyExcelorStata,butthestructureofthosedatahindersanalysisaspaneldata.Forarecentyear,theheaderlineoftheCSV leis"Seriescode","CountryCode","CountryName","1960","1961","1962","1963","1964","1965","1966","1967","1968","1969","1970","1971","1972","1973","1974","1975","1976","1977","1978","1979","1980","1981","1982","1983","1984","1985","1986","1987","1988","1989","1990","1991","1992","1993","1994","1995","1996","1997","1998","1999","2000","2001","2002","2003","2004"1.Seehttp://econ.worldbank.org. 270Statatip45Thatis,eachrowoftheCSV lecontainsavariableandcountrycombination,withthecolumnsrepresentingtheelementsofthetimeseries.2Ourtargetdatasetstructureisthatappropriateforpanel-datamodeling,withthevariablesascolumnsandrowslabeledbycountryandyear.Twoapplicationsofreshapewillagainbeneededtoreachthetargetformat.We rstinsheet(see[D]insheet)thedataandtransformthetriliteralcountrycodeintoanumericcodewiththecountrycodesaslabels:.insheetusingwdiex.raw,commanames.encodecountrycode,generate(cc).dropcountrycodeWethenmustaddressthatthetime-seriesvariablesarenamedvar4-var48,astheheaderlineprovidedinvalidStatavariablenames(numericvalues)forthosecolumns.Weuserename(see[D]rename)tochangev4tod1960,v5tod1961,andsoon:forvi=4/48{renamev`i'd`=1956+`i''}Wenowarereadytocarryoutthe rstreshape.Wewanttoidentifytherowsofthereshapeddatasetbybothcountrycode(cc)andseriescode,thevariablename.ThereshapelongwilltransformafragmentoftheWDIdatasetcontainingtwoseriesandfourcountries:.reshapelongd,i(ccseriescode)j(year)(note:j=1960196119621963196419651966196719681969197019711972�197319741975197619771978197919801981198219831984198519861987�198819891990199119921993199419951996199719981999200020012002�20032004)Datawide�-longNumberofobs.7�-315Numberofvariables48�-5jvariable(45values)�-yearxijvariables:d1960d1961...d2004�-d2.Avariationoccasionallyencounteredwillresemblethisstructure,butwithperiodsinreversechronologicalorder.Thesolutionherecanbeusedtodealwiththatproblemaswell. C.F.BaumandN.J.Cox271.listin1/15ccseriesc~eyearcountrynamed1.AFGadjnetsav1960Afghanistan.2.AFGadjnetsav1961Afghanistan.3.AFGadjnetsav1962Afghanistan.4.AFGadjnetsav1963Afghanistan.5.AFGadjnetsav1964Afghanistan.6.AFGadjnetsav1965Afghanistan.7.AFGadjnetsav1966Afghanistan.8.AFGadjnetsav1967Afghanistan.9.AFGadjnetsav1968Afghanistan.10.AFGadjnetsav1969Afghanistan.11.AFGadjnetsav1970Afghanistan-2.9712912.AFGadjnetsav1971Afghanistan-5.5451813.AFGadjnetsav1972Afghanistan-2.4072614.AFGadjnetsav1973Afghanistan-.18828115.AFGadjnetsav1974Afghanistan1.39753Therowsofthedataarenowlabeledbyyear,butoneproblemremains:allvariablesforagivencountryarestackedvertically.Tounstackthevariablesandputtheminshapeforxtreg(see[XT]xtreg),wemustcarryoutasecondreshapethatspreadsthevariablesacrossthecolumns,specifyingccandyearastheivariablesandseriescodeasthejvariable.Sincethatvariablehasstringcontent,weusethestringoption..reshapewided,i(ccyear)j(seriescode)string(note:j=adjnetsavadjsavC02)Datalong�-wideNumberofobs.315�-180Numberofvariables5�-5jvariable(2values)seriescode�-(dropped)xijvariables:d�-dadjnetsavdadjsavC02.ordercccountryname.tssetccyearpanelvariable:cc(stronglybalanced)timevariable:year,1960to2004Afterthistransformation,thedataarenowinshapeforxtmodeling,tabulation,orgraphics.Asillustratedhere,thereshapecommandcantransformeventhemostinconvenientdatastructureintothestructureneededforyourresearch.Itmaytakemorethanoneapplicationofreshapetogettherefromhere,butitcandothejob.