Sometimes, we might wish to visualize the effect of applying a mathematical function to a set of values, instead of the original variable itself. In this recipe, we will learn a simple method to plot functions of variables.
We will use the base graphics library for this recipe, so all you need to do is run the recipe at the R prompt. It is good practice to save your code as a script for use again later.
Let's say we want to plot the difference in rainfall between Tokyo and London. We can do this just by passing the correct expression to the plot() function:
rain <- read.csv("cityrain.csv")
plot(rain$Berlin-rain$London,type="l",lwd=2,
xaxt="n",col="blue",
xlab="Month",ylab="Difference in Rainfall (mm)",
main="Difference in Rainfall between Berlin and London (Berlin-London)")
axis(1,at=1:length(rain$Month),labels=rain$Month)
abline(h=0,col="red")