r - R 中 Monty Hall 问题的蒙特卡罗模拟不起作用？

Question

我正在 R 中编写一个函数来对 Monty Hall 问题执行蒙特卡罗模拟。当门没有开关时，该函数正在工作 switch == FALSE，但是当我调用 mean(replicate(10000, monty_hall(switch = TRUE))) 时，预期答案约为 0.66，但实际上我得到了 0.25 左右。

这是该函数的代码:

monty_hall = function(switch = logical()){
    doors <- c(1,2,3)
    names(doors) <- rep(c("goat", "car"), c(2,1))
    prize_door <- doors[3]

    guess <- sample(doors, 1)
    revealed_door <- sample(doors[!doors %in% c(guess, prize_door)],1)
    if(switch){
        switched_door <- sample(doors[!doors %in% c(guess, revealed_door)],1)
        prize_door == switched_door
    } else {
        prize_door == guess
        }
}

我应该进行哪些更改才能获得大约 0.66 的正确输出？

Answer 1

只需将门向量更改为字符即可

monty_hall = function(switch = logical()){
   doors <- c("1","2","3")
   names(doors) <- rep(c("goat", "car"), c(2,1))
   prize_door <- doors[3]

   guess <- sample(doors, 1)
   revealed_door <- sample(doors[!doors %in% c(guess, prize_door)],1)
   if(switch){
      switched_door <- sample(doors[!doors %in% c(guess, revealed_door)],1)
      prize_door == switched_door
   } else {
      prize_door == guess
   }
}

假设该人选择了 1 号门，奖品在 2 号门，那么剩下要揭晓的是 3 号门。

您将拥有revealed_door <- sample(3,1)这并不像你期望的那样工作，这变成 revealed_door <- sample(c(1,2,3),1)

在函数文档中，只需输入 ?sample

If x has length 1, is numeric (in the sense of is.numeric) and x >= 1, sampling via sample takes place from 1:x. Note that this convenience feature may lead to undesired behaviour when x is of varying length in calls such as sample(x)

我认为最简单的解决方法是更改​​为字符，但如果您必须使用数值，只需检查向量的长度并返回该值(如果为 1)，否则进行示例