[R] Indexing within by statement - different coloured lines in abline wanted..

John Kane jrkrideau at inbox.com
Mon May 27 15:08:17 CEST 2013

Slightly diffferent approach but will this do what you want.

  ggplot(Data1, aes(Predictor, Response1, colour = Site)) +
     geom_smooth(method= "lm", se = FALSE) +
     ggtitle("Raw data with linear regresssions by Site")

John Kane
Kingston ON Canada

> -----Original Message-----
> From: tom.wilding at sams.ac.uk
> Sent: Mon, 27 May 2013 10:39:58 +0000
> To: r-help at r-project.org
> Subject: [R] Indexing within by statement - different coloured lines in
> abline wanted..
> Dear R-list
> I'm trying to get each regression line, plotted using abline, to be of a
> different colour as the following code illustrates.  I'm hoping there is
> a simple indexing solution.  Many thanks.
> ## code from here
> colours=c("black","red","blue","green","pink")
> Mean=500;Sd=10;NosSites=5;Xaxis=seq(1,5,1)
> SlopeCoefficient=5;Site=(gl(NosSites,length(Xaxis),labels=1:NosSites))
> Predictor=rep(Xaxis,NosSites)
> InterceptAdjustment=rnorm(n=NosSites,mean=Xaxis,sd=50)
> RandomIntercept=rep(InterceptAdjustment,each=length(Xaxis))
> PreResponse=rnorm(n=length(Predictor),
> mean=Mean+SlopeCoefficient*1:length(Xaxis),sd=Sd)
> Response1=PreResponse+RandomIntercept
> #create data frame
> Data2=data.frame(Site,Predictor,Mean,SlopeCoefficient,RandomIntercept,Response1)
> Data1=data.frame("Site"=Data2$Site,"Predictor"=Data2$Predictor,"Response1"=Data2$Response1)
> #plotting
> var=as.numeric(levels(Data1$Site))
> par(mfrow=c(1,3))
> plot(Response1~Predictor,data=Data1,xlim=c(min(Xaxis),max(Xaxis)),ylim=c(MN,MX),
>      pch=as.numeric(Site),main="Raw data with linear regresssions by
> Site")
> by(Data1,Data1$Site,function(Site){
>   par(new=T)
>   abline(lm(Response1~Predictor,data=Site),col=colours[])#index in here.
> })
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