R switch()如何将案例与向量进行比较？

Question

我在 R 中的 switch 语句有一点问题。下面的代码就OK了……:

    value = "B"
  switch(value, 
         "A"={
           print("value = A")
         },
         "B"={
           print("value = B")
         },
         "C"={
           print("value = C")
         },
         {
           print("Other !!!")
        }
        )

它返回:

[1] "value = B"

...但我想将值与向量的值进行比较，如下所示:

mychr = c("A","B", "C")
  value = "B"
  switch(value, 
         mychr[1]={
           print(mychr[1])
         },
         mychr[2]={
           print(mychr[2])
         },
         mychr[3]={
           print(mychr[3])
         },
         {
           print("Other !!!")
         }
         )

这行不通。

我可以用“if else”或第一个代码来做到这一点，但我想理解错误。

Answer 1

我确定有更简单的方法，但您可以使用 alist 和 do.call

xlist = c("A","B", "C")
value = "B"
myList <- alist(print(xlist[1]), print(xlist[2]), print(xlist[3]), print("Other !!!"))
myList <- setNames(myList, c(xlist, ''))
do.call(switch, c(EXPR = value, myList))

例子:

> value = "D"
> do.call(switch, c(EXPR = value, myList))
[1] "Other !!!"
> value = "A"
> do.call(switch, c(EXPR = value, myList))
[1] "A"
> value = "C"
> do.call(switch, c(EXPR = value, myList))
[1] "C"
> value = "B"
> do.call(switch, c(EXPR = value, myList))
[1] "B"