How to draw a contour plot when data are not on a regular grid?

Question

Say I have 3 variables such that

x=1:9
y=c(1,1,1,2,2,2,3,3,3)
z=6:14

How can I rearrange the data so that I can make a contour plot of the

Answer 1

z is a matrix of values where contour lines are to be drawn. x and y are their respective location. "Tyler" at r-help mailing list explains this and gives an example of how to transform your data to make things work. See also examples in the help of ?contour.

x = seq(0, 10, by = 0.5)
y = seq(0, 10, by = 0.5)
z <- outer(x, y)

contour(x, y, z)