R/plot_ss.R

In dundeemath/MA22004labs: MA22004 (University of Dundee)

#' @export
plot_ss <- function(x, y, showSquares = FALSE, leastSquares = FALSE){
 plot(y~x, asp = 1)# xlab = paste(substitute(x)), ylab = paste(substitute(y)))

 if(leastSquares){
  m1 <- lm(y~x)
  y.hat <- m1$fit
 } else{
  cat("Click two points to make a line.")
  pt1 <- locator(1)
  points(pt1$x, pt1$y, pch = 4)
  pt2 <- locator(1)
  points(pt2$x, pt2$y, pch = 4)
  pts <- data.frame("x" = c(pt1$x, pt2$x),"y" = c(pt1$y, pt2$y))
  m1 <- lm(y ~ x, data = pts)
  y.hat <- predict(m1, newdata = data.frame(x))
 }
 r <- y - y.hat
 abline(m1)

 oSide <- x - r
 LLim <- par()$usr[1]
 RLim <- par()$usr[2]
 oSide[oSide < LLim | oSide > RLim] <- c(x + r)[oSide < LLim | oSide > RLim] # move boxes to avoid margins

 n <- length(y.hat)
 for(i in 1:n){
  lines(rep(x[i], 2), c(y[i], y.hat[i]), lty = 2, col = "blue")
  if(showSquares){
   lines(rep(oSide[i], 2), c(y[i], y.hat[i]), lty = 3, col = "orange")
   lines(c(oSide[i], x[i]), rep(y.hat[i],2), lty = 3, col = "orange")
   lines(c(oSide[i], x[i]), rep(y[i],2), lty = 3, col = "orange")
  }
 }

 SS <- round(sum(r^2), 3)
 cat("\r                                ")
 print(m1)
 cat("Sum of Squares: ", SS)
}