reilly media] r cookbook useful tricks

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1、CHAPTER12UsefulTricksIntroductionTherecipesinthischapterareneitherobscurenumericalcalculationsnordeepstatis-ticaltechniques.Yettheyareusefulfunctionsandidiomsthatyouwilllikelyneedatonetimeoranother.12.1PeekingatYourDataProblemYouhavealotofdata—toomuchtodisplayatonce.Nonetheless

2、,youwanttoseesomeofthedata.SolutionUseheadtoviewthefirstfewdataorrows:>head(x)Usetailtoviewthelastfewdataorrows:>tail(x)DiscussionPrintingalargedatasetispointlessbecauseeverythingjustrollsoffyourscreen.Useheadtoseealittlebitofthedata:>head(dfrm)xyz10.75331100.57562846-0.1710760

3、22.01435470.833122740.36985843-0.35513450.574715422.013234842.02816780.78945319-0.53788543135-2.21687450.017580241.834487960.7583962-1.782147552.2848990Usetailtoseethelastfewrowsandthenumberofrows.Here,weseethatthisdataframehas10,120rows:>tail(dfrm)xyz10115-0.0314354-0.74988291

4、-0.204896310116-0.47790010.934075101.050997710117-1.13144021.893084171.7207972101180.4891881-1.20792811-1.4630227101191.2349013-0.09615198-0.988751310120-1.3763834-2.253096280.9296106SeeAlsoSeeRecipe12.15forseeingthestructureofyourvariable’scontents.12.2WidenYourOutputProblemYo

5、uareprintingwidedatasets.Riswrappingtheoutput,makingithardtoread.SolutionSetthewidthoptiontoreflectthetruenumberofcolumnsinyouroutputwindow:>options(width=numcols)DiscussionBydefault,Rformatsyouroutputtobe80columnswide.It’sfrustratingwhenyouprintawidedatasetandRwrapstheoutputli

6、nesaccordingtoitsassumedlimitationof80columns.Yourexpensive,wide-screendisplaycanprobablyaccommodatemanymorecolumnsthanthat.Ifyourdisplayis120characterswide,forexample,thenaskRtousetheentire120columnsbysettingthewidthoption:>options(width=120)NowRwillwrapitslinesafter120charact

7、ers,not80,lettingyoucomfortablyviewwiderdatasets.SeeAlsoSeeRecipe3.16formoreaboutsettingoptions.314

8、Chapter12:UsefulTricks12.3PrintingtheResultofanAssignmentProblemYouareassigningavaluetoavariableandyouwanttoseeitsvalue.SolutionSimplyputparenthesesaroundtheassignment:>x<-1/pi#P

9、rintsnothing>(x<-1/pi)#Printsassignedvalue[1]0.3183099