stat_contour not able to generate contour lines

Question

I need to add lines via stat_contour() to my ggplot/ggplot2-plot. Unfortunately, I can not give you the real data from which point val

Answer 1

You should generate a z for each combination of x and y using expand.grid or outer. For example:

library(ggplot2)
testPts <- transform(expand.grid(x=1:10,y=1:5),z=sin(x*y))
(ggplot(data=testPts, aes(x=x, y=y, z=z))
 + stat_contour()
 + geom_point(aes(colour=z))
)