Create live x-y scatter plot with correlation and regression line

scatter_play.R

scatter_play <- function() {
  # create a blank plot (use and then remove a fake point)
  points = data.frame(x=c(-99), y=c(-99))
  plot(points, xlim=c(-5,50), ylim=c(-5,50))
  points = data.frame(x=c(), y=c())
  
  cat("Click on plot to add points; [Esc] to quit")
  repeat {
    location <- locator(1)
    
    if (is.null(location)) break
    points <- rbind(points, location)
    plot(points, xlim=c(-5,50), ylim=c(-5,50),
         pch = 16, col=rgb(0.5, 0.5, 0.5, 0.5))
    
    if (nrow(points) < 2) next 
    abline(lm(points$y ~ points$x), 
           col=rgb(0.0, 0.0, 0.5, 0.5), lwd=2)
    text(0, 48, paste("r: ", round(cor(points$x, points$y), 2)))
  }
}