Question

Is it possible to add more than one x-axis to a plot in R? And to put an annotation next to each scale?

Edit > here’s the result of Nick Sabbe idea. For the annotation (a little text at the left of each axis), is it possible ?

Answer 1

You can use the line argument of axis() to place an axis higher or lower, this way you can make multiple axes. With mtext() you can then add a label to the side. Do note that the plot itself is only on one scale so you need to rescale the points and labels of the other scale accordingly:

# Plot and first axis:
plot(1:10,1:10,bty="n",col="red",pch=16,axes=FALSE,xlab="",ylab="")
axis(2,0:11,las=1)
axis(1,0:11,line=1,col="red",col.ticks="red",col.axis="red")
mtext("Label 1",1,line=1,at=0.2,col="red")

# Secondary points and axis:
points(rnorm(10,50,20)/10, rnorm(10,5,2),pch=16, col="blue" )
axis(1,0:11,labels=0:11*10,line=3,col="blue",col.ticks="blue",col.axis="blue")
mtext("Label 2",1,line=3,at=0.2,col="blue")