#-*- R -*-

library(MASS)
library(class)
library(nnet)


Pop<-read.table("ex08.dat")
names(Pop)<-c("x1","x2","y")

#decrease len if you have little memory.

decplot <- function(xp, yp, Z, t)
{
    plot(Pop[, 1], Pop[, 2], xlim=c(-6.0,10), ylim=c(-6,10), type = "n", xlab = "x1", ylab = "x2")
	title(t)
    for(il in 1:2) {
        set <- Pop$y==levels(Pop$y)[il]
        text(Pop[set, 1], Pop[set, 2],
             labels = as.character(Pop$y[set]), col = 2 + il) }
    zp <- Z[, 1] - Z[, 2]
    contour(xp, yp, matrix(zp, np), add = T, levels = 0, labex = 0)
    invisible()
}

p <- as.matrix(Pop[, -3])
tp <- Pop$y

xp <- seq(-6.0, 10.0, length = 10); np <- length(xp)
yp <- seq(-6.0, 10.0, length = 10)

pt <- expand.grid(x1 = xp, x2 = yp)

par(mfcol=c(1,2))

Z <- knn(p, pt, tp, k = 1)
decplot(xp, yp, class.ind(Z),"k=1")

Z <- knn(p, pt, tp, k = 3)
decplot(xp, yp, class.ind(Z),"k=3")