R/addhlines.R

In gamclass: Functions and Data for a Course on Modern Regression and Classification

addhlines <-
function(x,y, ...){
  ordx <- order(x)
  xo <- x[ordx]
  yo <- y[ordx]
  breaks <- diff(yo)!=0
  xh <- c(xo[1],0.5*(xo[c(FALSE,breaks)]+xo[c(breaks, FALSE)]))
  yh <- yo[c(TRUE, breaks)]
  y3 <- x3 <- numeric(3*length(xh)-1)
  loc1 <- seq(from=1, to=length(x3), by=3)
  x3[loc1] <- xh
  x3[loc1+1]<- c(xh[-1], max(x))
  x3[loc1[-length(loc1)]+2] <- NA
  y3[loc1[-length(loc1)]+2] <- NA
  y3[loc1] <- yh
  y3[loc1+1] <- yh
  lines(x3,y3, ...)
}