Question

once again Im confronted with a complicated ggplot. I want to plot different plottypes within one plot using facet grid.

I hope I can make my point clear using the following example:
I want to produce a plot similar to the first picture but the upper plot should look like the second picture.
I already found the trick using the subset function but I can’t add vertical lines to only one plot let alone two or three (or specify the color).

CODE:

a <- rnorm(100)
b <- rnorm(100,8,1)
c <- rep(c(0,1),50)


dfr <- data.frame(a=a,b=b,c=c,d=seq(1:100))
dfr_melt <- melt(dfr,id.vars="d")

#I want only two grids, not three
ggplot(dfr_melt,aes(x=d,y=value)) + facet_grid(variable~.,scales="free")+
geom_line(subset=.(variable=="a")) + geom_line(subset=.(variable=="b"))

#Upper plot should look like this
ggplot(dfr,aes(x=d,y=a)) + geom_line() + geom_line(aes(y=c,color="c"))+
geom_hline(aes(yintercept=1),linetype="dashed")+
geom_hline(aes(yintercept=-2),linetype="dashed")

Answer 1

If I understand your question correctly, you just need to a variable column to dfr in order to allow the faceting to work:

dfr$variable = "a"
ggplot(subset(dfr_melt, variable=="a"),aes(x=d,y=value)) +  
  facet_grid(variable~.,scales="free")+
  geom_line(data=subset(dfr_melt,variable=="a"))  + 
  geom_line(data=subset(dfr_melt, variable=="b")) + 
  geom_line(data=dfr, aes(y=c, colour=factor(c))) + 
  geom_hline(aes(yintercept=1),linetype="dashed")+
  geom_hline(aes(yintercept=-2),linetype="dashed")

Notice that my plot doesn’t have the zig-zig line, this is because I changed:

  #This is almost certainly not what you want
  geom_line(data=dfr, aes(y=c, colour="c"))

to

  #I made c a factor since it only takes the values 0 or 1
  geom_line(data=dfr, aes(y=c, colour=factor(c)))
  ##Alternatively, you could have
  geom_line(data=dfr, aes(y=c), colour="red") #or
  geom_line(data=dfr, aes(y=c, colour=c)) #or