search for: inadverdently

Consider the following examples: library(lattice) x = c(1,1,2,2) y = c(1,2,1,2) z = 1:4 levelplot(z~x+y,at=c(.5, 1.5, 2.5, 3.5, 4.5)) # correct levelplot(z~x+y,at=c(.5, 1.5, 2.5)) # ? The second plot is clearly incorrect. However, I don't know what correct behaviour is: ignore everything above 2.5 and issue a warning? Reject at values that do not cover the data range, and issue an