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

[David Winsemius]

On Mar 25, 2011, at 4:19 PM, Pam Allen wrote:

> 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)

Oh my lord, that looks way, way too complicated! Why not do it with  
your previous dataset and replace your `levels` misdirection with a  
correct method  for the goal that I never saw articulated in standard  
English. The findInterval function can be used as an index to a color  
vector to he a color-encoded height:

date=c(1:300)
flow=sin(2*pi/53*c(1:300))
dat=cbind.data.frame(date, flow)  ### Three lines

with(dat,plot(date,flow,type="n"))
with(dat, segments(date[1:299],flow[1:299],  # starting points for  
segments
                     date[2:300],flow[2:300],  # ending points offset  
by 1
             col=c("purple","green","blue", "red")[
                            findInterval(flow[1:299],  
c(-1,0,.75,.85,1))]))

See attached: (Don't need no steenking `levels`.)
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>
> 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
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Help-with-plotting-a-line-that-is-multicoloured-based-on-levels-of-a-factor-tp3385857p3406309.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT