xgap <- ifelse(x > 8, x-6, x)
#Possibly you'd want to check if there are values between 2 and 8.
plot(xgap, y, col='blue', pch=16, xlab= 'x', ylab='y, z', xaxt="n")
points(xgap, z, col='red', pch=17)
xat <- pretty(xgap)
xat <- xat[xat!=2]
xlab <- ifelse(xat>2, xat+6, xat)
axis(1,at=xat, labels=xlab)
library(plotrix)
axis.break(1,2,style="slash")
Don't do this. gap.plot
provides a slightly better alternative, but I would probably use facets, e.g., with ggplot2.