[R] Help with plotting a line that is multicoloured based on levels of a factor

[Pam Allen]

Hello again, 

I wrote an example that better represents my data, since the coloured points
are actually consecutive, but with variable lengths:

date=as.Date(c(1:300))
flow=sin(2*pi/53*c(1:300))
levels=c(rep(c("high","med","low"),100))
data=cbind.data.frame(date, flow, levels)

library(zoo)
z <- zoo(data$flow, data$date)
zz=cbind.data.frame(date=as.Date(rownames(cbind.data.frame(rollapply(z, 2,
align = "right", FUN="+")))),flow.change=(rollapply(z, 2, align =
"right",FUN="+" )))
names(zz)=c("date","todays.flow","next.day.flow")
zzz=cbind.data.frame(zz[,1], (zz[,3]-zz[,2]))
names(zzz)=c("date","change.flow") 
data2=merge(data, zzz)
rate=zoo(data2$change.flow,data2$date)
x=cbind.data.frame(date=as.Date(rownames(cbind.data.frame(rollapply(rate, 2,
align="left", FUN="+")))), sign=rollapply(rate, 2, align="left",FUN="+"))  
names(x)=c("date","todays.change","next.day.change") 
xx=cbind.data.frame(x[,1],(x[,3]*x[,2]))
names(xx)=c("date","sign") 
data2=merge(data2, xx)

data3=cbind(data2,pass1=
	ifelse(data2$flow<0, "extreme.low",
	ifelse(data2$flow>=0.9, "extreme.high","NA")))  
data4=cbind(data3, pass2=

ifelse(data3$flow<0.8&data3$flow>0&data3$change.flow>=0&data3$change>=0&data3$pass1=="NA","medium"
, 

ifelse(data3$flow<0.7&data3$flow>0&data3$change.flow<0&data3$change<0&data3$pass1=="NA","medium","NA"))) 
data4$pass1=paste(data4$pass1, data4$pass2)
data4$pass1=replace(data4$pass1, data4$pass1=="NA NA", "low")

dat=cbind(data4[,1:5], class=
	ifelse(data4$pass1=="extreme.high NA","1.Extreme.High",
	ifelse(data4$pass1=="NA medium","2.Medium",
	ifelse(data4$pass1=="low","3.Low",
	ifelse(data4$pass1=="extreme.low NA","4.Extreme.Low",NA)))))

colour=ifelse(dat$class=="1.Extreme.High","red",
               ifelse(dat$class=="2.Medium","green",
               ifelse(dat$class=="3.Low","blue",
		ifelse(dat$class=="4.Extreme.Low","purple",""))))
plot(dat$date, dat$flow, col=colour) 


What I would like to do is to plot this using a line with the correct
colours instead of points, i.e.:

plot(dat$date, dat$flow, col=colour, type="l") ##Doesn't work, because the
line is continuous

Any help would be much appreciated.  Thank you!

-Pam 

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