gamclass (version 0.62.3)

addhlines: Add horizontal lines to plot.

Description

This is designed for adding horizontal lines that show predicted values to a plot of observed values versus x-values, in rpart regression. Where predicted values change between two successive x-values lines are extended to the midway point. This reflects the way that predict.rpart handles predictions for new data.

Usage

addhlines(x, y, ...)

Value

Lines are added to the current graph.

Arguments

x

Vector of predictor variable values.

y

Vector of predicted values.

...

Additional graphics parameters, for passing through to the lines() function.

Author

John Maindonald

Examples

x <- c(34, 18, 45, 18, 27, 24, 34, 20, 24, 28, 21, 18)
y <- c(14, 11, 12, 9, 4, 11, 6, 9, 4, 10, 9, 2)
hat <- c(10.5, 7.75, 10.5, 7.75, 7, 7, 10.5, 7.75, 7, 10.5, 7, 7.75)
plot(x, y)
addhlines(x, hat, lwd=2, col="gray")

## The function is currently defined as
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, ...)
}