overlaid plots using different axes in R

Question

I am trying to overlay two graphs onto the same axes. I set up my axes limits and labels first, but then when I plot the graphs they resize and are not on my pre-determined scale.

I have pared my code down into a simple example. You can see that 100 and 10 are showing up at the same place on the y axis. Please help!

x<- 1:3
y1<- c(100, 75, 20)
y2<- c(10, 9, 4)

plot.new()                              
plot(0, type="n",    
     xlim=c(1,max(x)), ylim=c(0,max(y1,y2)),
     xlab= "x label", ylab= "y label", main= "This stupid graph doesn't work!")
par(new=TRUE)
par(new=TRUE)
plot(x,y1, type="b", pch=19, col="orchid", 
     axes=FALSE, ann=FALSE)
par(new=TRUE)
plot(x,y2, type="b", pch=19, col="slateblue", 
     axes=FALSE, ann=FALSE)
legend("topright",c("This is","Annoying"), col=c("orchid","slateblue"), pch=19)

Answer 1

You want to use lines to add the second line, meanwhile making sure that ylim allows for all the values being plotted to fit within the plotting region.

plot(y1 ~ x, ylim = range(c(y1, y2)), xlab = "x label", ylab = "y label",
       main = "This one might work!", type = 'b', pch = 19, col = "orchid")
lines(y2, type = 'b', pch = 19, col = 'slateblue')
legend("topright", c("R is", "awesome"), col = c("orchid","slateblue"), pch = 19)