添加到卷曲参数

Question

我试图用这个典型的例子来说明卷曲运算符的工作原理

mean_by <- function(data, by, var) {
  data %>%
    dplyr::group_by({{ by }}) %>%
    dplyr::summarise(avg = mean({{ var }}, na.rm = TRUE))
}

mtcars %>% mean_by(by = cyl, var = disp)

并通过向分组添加附加变量来修改它。唉，我可能永远无法理解那个运算符实际上做了什么；我尝试做类似的事情

mean_by <- function(data, by, var) {
  data %>%
    dplyr::group_by({{ c(by, hp) }}) %>%
    dplyr::summarise(avg = mean({{ var }}, na.rm = TRUE))
}

mtcars %>% mean_by(by = cyl, var = disp)

显然不起作用

Answer 1

如果您想编写一个函数来按

hp

以及传递给它的其他任何内容进行分组，那么使用

...

:

会更容易

mean_by_hp <- function(data, ..., var) {
    data |>
        dplyr::group_by(hp, ...) |>
        dplyr::summarise(avg = mean({{ var }}, na.rm = TRUE))
}


mean_by_hp(mtcars, cyl, var = disp)
#       hp   cyl   avg
#    <dbl> <dbl> <dbl>
#  1    52     4  75.7
#  2    62     4 147.
#  3    65     4  71.1
#  4    66     4  78.8
#  5    91     4 120.
#  6    93     4 108
#  7    95     4 141.
#  8    97     4 120.
#  9   105     6 225
# 10   109     4 121