在dplyr链中使用table()

Question

有人可以解释为什么table()在dplyr-magrittr管道操作链中不起作用？这是一个简单的代表:

tibble(
  type = c("Fast", "Slow", "Fast", "Fast", "Slow"),
  colour = c("Blue", "Blue", "Red", "Red", "Red")
) %>% table(.$type, .$colour)

sort.list(y)出错:'x'必须是'sort.list'的原子'你有没有在列表上调用'sort'？

但这当然有效:

df <- tibble(
  type = c("Fast", "Slow", "Fast", "Fast", "Slow"),
  colour = c("Blue", "Blue", "Red", "Red", "Red")
) 

table(df$type, df$colour)


       Blue Red
  Fast    1   2
  Slow    1   1

Answer 1

此行为是设计使然:https://github.com/tidyverse/magrittr/blob/00a1fe3305a4914d7c9714fba78fd5f03f70f51e/README.md#re-using-the-placeholder-for-attributes

既然你没有.它自己,那么仍然会将tibble作为第一个参数传递,所以它更像是

... %>% table(., .$type, .$colour)

官方的magrittr解决方案是使用花括号

... %>% {table(.$type, .$colour)}

Answer 2

我已经习惯with(table(...))这样使用：

tibble(type = c("Fast", "Slow", "Fast", "Fast", "Slow"),
       colour = c("Blue", "Blue", "Red", "Red", "Red")) %>% 
  with(table(type, colour))

类似于我们读作%>%“然后”的方式，我将其读作“然后用该数据制作这个表”。

Answer 3

该%>%运营商dplyr实际上是从进口magrittr。使用magrittr，我们还可以使用%$%运算符，它公开上一个表达式中的名称：

library(tidyverse)
library(magrittr)

tibble(
  type = c("Fast", "Slow", "Fast", "Fast", "Slow"),
  colour = c("Blue", "Blue", "Red", "Red", "Red")
) %$% table(type, colour)

输出：

      colour
type   Blue Red
  Fast    1   2
  Slow    1   1