AdaBoost のアニメーション

AdaBoostM1.R

f <- function(X) {
  X <- as.matrix(X)
  limit <- qchisq(0.5, df = ncol(X))
  apply(X, 1, function(row) { 
    if(sum(row^2) > limit) 1 else -1 
  })
}

D <- 2
M <- 200
N <- 2000
set.seed(314)
X <- matrix(rnorm(N * D), nrow = N)
y <- f(X)

plot(X[,1], X[,2], col=y+2, pch=19)

library(rpart)
discrete_adaboost <- function(X, y, M) {
  N <- nrow(X)
  w <- rep(1/N, N)
  alpha_m <- double(M)
  Gm <- vector("list", length = M)
  for (i in seq_len(M)) {
    Gm[[i]] <- rpart(factor(y) ~ X, weights = w, maxdepth = 1)
    y_hat <- predict(Gm[[i]], type = "class")
    err <- y != y_hat
    err_m <- sum(err * w) / sum(w)
    alpha_m[i] <- log((1 - err_m) / err_m)
    w <- w * exp(alpha_m[i] * err)
  }
  list(alpha_m = alpha_m, Gm = Gm)
}

res <- discrete_adaboost(X, y, M = M)
predict_DA <- function(DA, n_iter) {
  pred <- vector("list", n_iter)
  for (i in seq_len(n_iter)) {
    pred[[i]] <- DA$alpha_m[[i]] * 
      as.integer(as.character(predict(DA$Gm[[i]], type = "class")))
  }
  ifelse(rowSums(data.frame(pred)) > 0, 1, -1)
}

library(ggplot2)
df <- data.frame(X, y = factor(y))
g1 <- ggplot(df, aes(X1, X2)) + 
  geom_point(aes(color = y)) + 
  xlab(NULL) + ylab(NULL) + 
  scale_color_discrete(guide=FALSE) + 
  ggtitle("正解")

library(animation)
library(cowplot)

animation::saveGIF({
  pb <- txtProgressBar(0, M, style = 3)
  count <- 30
  for (i in seq_len(M)) {
    setTxtProgressBar(pb, i)
    pred <- predict_DA(res, i)
    df <- data.frame(X, y = factor(pred))
    g2 <- ggplot(df, aes(X1, X2)) + 
      geom_point(aes(color = y)) + 
      xlab(NULL) + ylab(NULL) +
      scale_color_discrete(guide=FALSE) +
      ggtitle(glue::glue("AdaBoost (iter = {i})"))
    
    for (j in 1:count) {
      print(cowplot::plot_grid(g1, g2))
    }
    count <- if (i < 10) 10 else if (i < 20) 5 else 1
  }
  for (i in 1:50) {
    print(cowplot::plot_grid(g1, g2))
  }
}, movie.name = "AdaBoostAnimation2.gif", interval = 0.1, 
ani.width = 600, ani.height = 320)