Question

我正在尝试编写一个R脚本来根据范围内的值拟合来评估不同的表达式。我们的想法是，如果长度在一个范围内，它将以一种方式进行评估，如果它在更长的范围内，它将以不同的方式进行评估。

我可以使用if / else语句来完成这项工作，但它非常难看，而且我确信必须有更好的方法......这里的代码可以运行。

Length=8.2

if (Length<1) 
    mode="Walk"
else if (1<=Length & Length <5)
    mode="bike" 
else if (5<=Length & Length <10)
    mode="drive"
else if (Length>=10)
    mode="fly"

我一直在尝试使用switch函数做一些工作，但它似乎只能用于文本或整数...有没有办法让switch语句在每种情况下进行评估，例如？ / p>

Length=3.5

switch(Length,
       (Length<1)  mode="Walk"
       (1<=Length & Length <5)  mode="bike"
       (5<=Length & Length <10)  mode="drive"
       (Length=>10)  mode="fly"
)

Answer 1

以下是Josh的类似答案，但使用findInterval：

Length <- 0:11

cuts <- c(-Inf, 1, 5, 10, Inf)
labs <- c("Walk", "bike", "drive", "fly")

labs[findInterval(Length, cuts)]
# [1] "Walk"  "bike"  "bike"  "bike"  "bike"  "drive" "drive"
# [8] "drive" "drive" "drive" "fly"   "fly"

你也可以使用嵌套的ifelse语句，这是一个品味问题：

ifelse(Length < 1,  "Walk",
ifelse(Length < 5,  "bike",
ifelse(Length < 10, "drive",
                    "fly")))
# [1] "Walk"  "bike"  "bike"  "bike"  "bike"  "drive" "drive"
# [8] "drive" "drive" "drive" "fly"   "fly"

Answer 2

cut()能做你需要的吗？

Length <- 0:11

cuts <- c(-Inf, 1, 5, 10, Inf)
labs <- c("Walk", "bike", "drive", "fly")

as.character(cut(Length, breaks = cuts, labels = labs, include.lowest=TRUE))
#  [1] "Walk"  "Walk"  "bike"  "bike"  "bike"  "bike"  "drive" "drive" "drive"
# [10] "drive" "drive" "fly"

Answer 3

使用dplyr的case_when声明：

> library(dplyr)
> Length=3.5
> mode <- case_when(
                (Length < 1) ~ "Walk",
                (1 <= Length & Length < 5) ~ "bike",
                (5 <= Length & Length < 10) ~ "drive",
                (Length >= 10) ~ "fly"
          )
> mode
[1] "bike"

Answer 4

剪切并切换：使用cut（）中的因子级别并将其传递到switch（）中以返回适当的代码。

 transport <- function(dist) {
   stopifnot(is.numeric(dist))
   x <- as.numeric(cut(dist, c(-Inf,0,1,5,10,Inf)), right = TRUE)
   switch (x,
           "No distance",
           "Walk",
           "Bike",
           "Drive",
           "Fly",
           stop("Not sure")
   )
 }

Answer 5

这个答案对于手头的例子来说算是过高了，但是它非常灵活-您可以在evaluate_like_this()内进行任何操作。

evaluate_one <- function(x) {
  switch(
    x,
    evaluate_like_this(x, "Walk"),
    evaluate_like_this(x, "No distance"),
    evaluate_like_this(x, "Bike"),
    evaluate_like_this(x, "Drive"),
    evaluate_like_this(x, "Fly")
  )
}

evaluate_like_this <- function(x, y) {
  paste0(x, ": ", y)
}

these_data <- 0:11
intervals <- cut(these_data, breaks = c(-Inf, 1, 5, 10, Inf), label = FALSE)
unlist(lapply(intervals, evaluate_one))
#>  [1] "1: Walk"        "1: Walk"        "2: No distance" "2: No distance"
#>  [5] "2: No distance" "2: No distance" "3: Bike"        "3: Bike"       
#>  [9] "3: Bike"        "3: Bike"        "3: Bike"        "4: Drive"

^{由reprex package（v0.2.1）于2018-12-19创建}

关于比较的R switch语句

5 个答案: