Question

I woud like to understand how levelplot works. I have almost no experience with plots and R.

What confuses me, is how should I interpret for example x~y*z ?
Lets assume I have a function, and I would like to show how often certain value occurs by using 3d plot. I would have hence x = x, y = f(x) and z = count. How to obtain such simple plot by using levelplot (or something else if it is not appriopriate).

In addition, should I group “count” myself – 3 columns in my data from, or just have 2 columns – x and f(x) and have duplications?

Hope my question is clear, I tried to read levelplot documentation, however I could not find any tutorial that teaches basics.

Answer 1

The following example is from the ?levelplot documentation.

The formula z~x*y means that z is a function of x, y and the interaction between x and y. Had the function been z~x+y it would have meant that z is a function of x and y, ignoring any interaction.

You can read more about the formula interface in the help for ?formula.

x <- seq(pi/4, 5 * pi, length.out = 100)
y <- seq(pi/4, 5 * pi, length.out = 100)
r <- as.vector(sqrt(outer(x^2, y^2, "+")))
grid <- expand.grid(x=x, y=y)
grid$z <- cos(r^2) * exp(-r/(pi^3))
levelplot(z~x*y, grid, cuts = 50, scales=list(log="e"), xlab="",
          ylab="", main="Weird Function", sub="with log scales",
          colorkey = FALSE, region = TRUE)