R语言使用%in%匹配列表异常：石头剪刀蜥蜴史波克游戏问题排查

我编写了一个用于玩“石头、剪刀、布、蜥蜴、史波克”的函数，通过menu()让用户选择选项，sample()生成电脑的选择，并预设10种获胜配对来判定胜负。代码运行无报错，但输出不符合预期，怀疑问题出在%in%的使用或list的特性上。

原代码 #

choices <- c("rock", "paper", "scissors", "lizard", "spock")

# Scissors [3] beats paper [2], 
# paper [2] beats rock [1], 
# rock [1] beats lizard [4], 
# lizard [4] beats Spock [5],
# Spock [5] beats scissors [3], 
# scissors [3] beats lizard [4], 
# lizard [4] beats paper [2], 
# paper [2] beats Spock [5], 
# Spock [5] beats rock [1], 
# rock [1] beats scissors [3].

wins <- list(c(3, 2), c(2, 1), c(1, 4), c(4, 5), c(5, 3), c(3, 4), c(4, 2), c(2, 5), c(5, 1), c(1, 3))

fun <- function(){
  input <- menu(choices, title="Choose one:")
  if (input == 0){
    message("You have to pick a valid choice to play this. Try again.")
  }
  if (input >= 1 && input <= 5){
    comp_choice <- sample(1:5, 1)
    message(paste0("you chose ", choices[input]))
    message(paste0("computer chose ", choices[comp_choice]))
    print(list(c(input, comp_choice)) %in% wins)
    if (input != comp_choice){
      if (list(c(input, comp_choice)) %in% wins) {
        message("you won")
        } 
      else message("you lost")
    }
    else message("it's a draw")
  }
}

fun()

异常输出示例（本应判定为胜利） #

Selection: 3
you chose scissors
computer chose lizard
[1] FALSE
you lost

问题原因 #

%in%在处理list元素时，无法直接正确匹配两个长度相同的向量。当你用list(c(input, comp_choice)) %in% wins时，R并不会逐个比较向量内的元素是否完全一致，而是做了更高层级的list元素匹配，导致明明存在的配对被判定为不存在。

解决方法 #

替换胜负判定的逻辑，使用sapply()遍历wins列表，检查是否有任何一个配对与c(input, comp_choice)完全相等。

修改后的代码 #

choices <- c("rock", "paper", "scissors", "lizard", "spock")

wins <- list(c(3, 2), c(2, 1), c(1, 4), c(4, 5), c(5, 3), c(3, 4), c(4, 2), c(2, 5), c(5, 1), c(1, 3))

fun <- function(){
  input <- menu(choices, title="Choose one:")
  if (input == 0){
    message("You have to pick a valid choice to play this. Try again.")
  }
  if (input >= 1 && input <= 5){
    comp_choice <- sample(1:5, 1)
    message(paste0("you chose ", choices[input]))
    message(paste0("computer chose ", choices[comp_choice]))
    # 替换判定逻辑
    user_wins <- any(sapply(wins, function(pair) all(pair == c(input, comp_choice))))
    print(user_wins)
    if (input != comp_choice){
      if (user_wins) {
        message("you won")
        } 
      else message("you lost")
    }
    else message("it's a draw")
  }
}

fun()

验证效果 #

当选择剪刀（3）、电脑选蜥蜴（4）时，c(3,4)是wins中的配对，此时user_wins会返回TRUE，正确判定为胜利。

内容的提问来源于stack exchange，提问作者FB001