モンティ・ホール問題のシミュレーション

MontyHall_problem.R

library(dplyr)
library(gt)

doors = LETTERS[1:3]
policy1 = 0L
policy2 = 0L
iter = 100000
res_raw = matrix(NA_character_, iter, 4)
set.seed(1124)
system.time({
  for(i in 1:iter){
    hit  = sample(doors,1)
    choice1  = sample(doors,1)
    open  = sample(setdiff(doors,c(hit,choice1)),1)
    choice2  = sample(setdiff(doors,c(open,choice1)),1)
    policy2 = policy2 + as.integer(choice2 == hit)
    policy1 = policy1 + as.integer(choice1 == hit)
    res_raw[i,] = c(hit,choice1,open,choice2)
  }  
})
#  user  system elapsed
# 3.129   0.012   3.213

print(policy1/iter) #0.33486 = 1/3
print(policy2/iter) #0.66514 = 2/3

colnames(res_raw) <- c("hit", "choice1", "open", "choice2")
res_sum <- as.data.frame(res_raw) %>% 
  group_by(hit,choice1,open,choice2) %>% 
  tally() %>% 
  ungroup() %>% 
  arrange(hit, choice1, open, choice2) %>% 
  mutate(prob = n/sum(n)) %>% 
  select(-n)

t1 = gt(res_sum)
t1
gtsave(t1,"tab1.png")