[英]Using switch statement within dplyr's mutate
我想在 dplyr 的 mutate 中使用 switch 语句。 我有一个简单的函数,它执行一些操作并通过 switch 分配替代值,例如:
convert_am <- function(x) {
x <- as.character(x)
switch(x,
"0" = FALSE,
"1" = TRUE,
NA)
}
当应用于标量时,这可以按需要工作:
>> convert_am(1)
[1] TRUE
>> convert_am(2)
[1] NA
>> convert_am(0)
[1] FALSE
我想通过mutate
调用得到等效的结果:
mtcars %>% mutate(am = convert_am(am))
这失败了:
mutate_impl(.data, dots)
错误:评估错误:EXPR 必须是长度为 1 的向量。
我知道这是因为传递给 switch 的值不是单一的,例如:
convert_am(c(1,2,2))
switch(x, 0 = FALSE, 1 = TRUE, NA)
:EXPR 必须是长度为 1 的向量
尝试矢量化也会产生预期的结果:
convert_am <- function(x) {
x <- as.character(x)
fun_switch <- function(x) {
switch(x,
"0" = FALSE,
"1" = TRUE,
NA)
}
vf <- Vectorize(fun_switch, "x")
}
>> mtcars %>% mutate(am = convert_am(am))
Error in mutate_impl(.data, dots) :
Column `am` is of unsupported type function
case_when
中的 case_when 并且我对使用它不感兴趣,我只对使switch
在 mutate 中工作感兴趣mutate_at
与作为传递的变量一起使用.
switch
未矢量化,因此为了提高效率,您需要使用ifelse
或case_when
- 但由于您的问题专门关于switch
,您可以通过矢量化来实现您想要的,例如
convert_am <- Vectorize(function(x) {
x <- as.character(x)
switch(x,
"0" = FALSE,
"1" = TRUE,
NA)
})
要么
convert_am <- function(x) {
x <- as.character(x)
sapply(x, function(xx) switch(xx,
"0" = FALSE,
"1" = TRUE,
NA))
}
它们都效率低下,因为它们涉及引擎盖下的循环。
This is simple enough to handle with ifelse directly:
Test <- tibble::tibble(
am = c(-1:5,NA,1, 0)
)
Test %>%
mutate(
newam = ifelse(am == 1, TRUE,
ifelse(am == 0, FALSE, NA))
)
With more categories, use a named vector:
Test %>%
mutate(
newam = ifelse(is.na(am) | !am %in% c(1,3,5), NA,
c("1" = "in1", "3" = "in3", "5" = "in5")[as.character(am)])
)
In fact if the value is not in the named list it will default to an NA
I think this will be pretty efficient
Test %>%
mutate(
newam = c("1" = "in1", "3" = "in3", "5" = "in5")[as.character(am)]
)
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