R語言 case when 函式

要點有兩個

不匹配的時候會返回 na，而不是保持不變

根據順序進行條件判斷，順序很重要

下面這段**，

x <- 1:50

case_when(
x %% 35 == 0 ~ "fizz buzz",
x %% 5 == 0 ~ "fizz",
x %% 7 == 0 ~ "buzz",
true ~ as.character(x)
)

[1] na          na          na          na          "fizz"      na         

[7] "buzz"      na          na          "fizz"      na          na         
[13] na          "buzz"      "fizz"      na          na          na         
[19] na          "fizz"      "buzz"      na          na          na         
[25] "fizz"      na          na          "buzz"      na          "fizz"     
[31] na          na          na          na          "fizz buzz" na         
[37] na          na          na          "fizz"      na          "buzz"     
[43] na          na          "fizz"      na          na          na         
[49] "buzz"      "fizz"

x <- 1:50

case_when(
x %% 35 == 0 ~ "fizz buzz",
x %% 5 == 0 ~ "fizz",
x %% 7 == 0 ~ "buzz",
true ~ as.character(x)
)#>  [1] "1"         "2"         "3"         "4"         "fizz"      "6"        
#>  [7] "buzz"      "8"         "9"         "fizz"      "11"        "12"       
#> [13] "13"        "buzz"      "fizz"      "16"        "17"        "18"       
#> [19] "19"        "fizz"      "buzz"      "22"        "23"        "24"       
#> [25] "fizz"      "26"        "27"        "buzz"      "29"        "fizz"     
#> [31] "31"        "32"        "33"        "34"        "fizz buzz" "36"       
#> [37] "37"        "38"        "39"        "fizz"      "41"        "buzz"     
#> [43] "43"        "44"        "fizz"      "46"        "47"        "48"       
#> [49] "buzz"      "fizz"     
# like an if statement, the arguments are evaluated in order, so you must
# proceed from the most specific to the most general. this won't work:
case_when(
true ~ as.character(x),
x %%  5 == 0 ~ "fizz",
x %%  7 == 0 ~ "buzz",
x %% 35 == 0 ~ "fizz buzz"
)#>  [1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10" "11" "12" "13" "14" "15"
#> [16] "16" "17" "18" "19" "20" "21" "22" "23" "24" "25" "26" "27" "28" "29" "30"
#> [31] "31" "32" "33" "34" "35" "36" "37" "38" "39" "40" "41" "42" "43" "44" "45"
#> [46] "46" "47" "48" "49" "50"

starwars %>%

select(name:mass, gender, species) %>%
mutate(
type = case_when(
height > 200 | mass > 200 ~ "large",
species == "droid"        ~ "robot",
true                      ~ "other"
))

case_character_type <- function(height, mass, species) 

case_character_type(150, 250, "droid")
#> [1] "large"
case_character_type(150, 150, "droid")
#> [1] "robot"

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要點有兩個 不匹配的時候會返回 na，而不是保持不變 根據順序進行條件判斷，順序很重要 下面這段 x 1 50 case when x 35 0 fizz buzz x 5 0 fizz x 7 0 buzz true as.character x 如果不包含true as.character x ...

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