reilly media] r cookbook graphics

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1、CHAPTER10GraphicsIntroductionGraphicsisagreatstrengthofR.Thegraphicspackageispartofthestandarddistri-butionandcontainsmanyusefulfunctionsforcreatingavarietyofgraphicdisplays.Thischapterfocusesonthosefunctions,althoughitoccasionallysuggestsotherpack-ages.Inthischapter’sSeeAlsosectionsImentionfunc

2、tionsinotherpackagesthatdothesamejobinadifferentway.Isuggestthatyouexplorethosealternativesifyouaredissatisfiedwiththebasicfunction.Graphicsisavastsubject,andIcanonlyscratchthesurfacehere.Ifyouwanttodelvedeeper,IrecommendRGraphicsbyPaulMurrell(Chapman&Hall,2006).Thatbookdiscussestheparadigmsbehi

3、ndRgraphics,explainshowtousethegraphicsfunctions,andcontainsnumerousexamples—includingthecodetorecreatethem.Someoftheexamplesareprettyamazing.TheIllustrationsThegraphsinthischapteraremostlyplainandunadorned.Ididthatintentionally.Whenyoucalltheplotfunction,asin:>plot(x)yougetaplain,graphicalrepre

4、sentationofx.Youcouldadornthegraphwithcolors,atitle,labels,alegend,text,andsoforth,butthenthecalltoplotbecomesmoreandmorecrowded,obscuringthebasicintention:>plot(x,main="ForecastResults",xlab="Month",ylab="Production",+col=c("red","black","green"))Iwanttokeeptherecipesclean,soIemphasizethebasicp

5、lotandthenshowlater(asinRecipe10.2)howtoaddadornments.221NotesonGraphicsFunctionsItisimportanttounderstandthedistinctionbetweenhigh-levelandlow-levelgraphicsfunctions.Ahigh-levelgraphicsfunctionstartsanewgraph.Itinitializesthegraphicswindow(creatingitifnecessary);setsthescale;maybedrawssomeadorn

6、ments,suchasatitleandlabels;andrendersthegraphic.Examplesinclude:plotGenericplottingfunctionboxplotCreateaboxplothistCreateahistogramqqnormCreateaquantile-quantile(Q-Q)plotcurveGraphafunctionAlow-levelgraphicsfunctioncannotstartanewgraph.Rather,itaddssomethingtoanexistinggraph:points,lines,text,

7、adornments,andsoforth.Examplesinclude:pointsAddpointslinesAddlinesablineAddastraightlinesegmentsAddlinesegmentspolygonAddaclosedpolygontextAddtextYoumustcallahigh-levelgraphicsroutinebeforecallingalow-levelgraphicsroutine.Th