tidyeval 函数和 `View()` 的问题

Question

代码块 #1 和 #2 相同，除了第 14 行。代码块 #1 使用 print() 调用，代码块 #2 使用 View() 调用。代码块 #1 工作正常。代码块 #2 给出错误 "Error in FUN(X[[i]], ...) : object 'cal.date' not found"。为什么？

1

library(tidyverse)
set.seed(1)
graph.data <- tibble(cal.date = as.Date(40100:40129, origin = "1899-12-30"), 
                     random_num = rnorm(30, 8, 5))

child_function <- function(df, variable, hor.line = 6) {  
  variable <- enquo(variable)
  df <- df %>% mutate(mutation = 2 * !!variable, horizontal.line = hor.line)
}

parent_function <- function(df, date, variable, hor.line = 6) {
  date <- enquo(date)
  variable <- enquo(variable)
  df <- df %>% child_function(!!variable, hor.line) %>% print()  # LINE 14
  p <- ggplot(df, aes(!!date, mutation)) + 
    geom_point() + 
    geom_hline(aes(yintercept = hor.line))
  p
}

parent_function(graph.data, date = cal.date, variable = random_num, hor.line = 8)

2

library(tidyverse)
set.seed(1)
graph.data <- tibble(cal.date = as.Date(40100:40129, origin = "1899-12-30"), 
                     random_num = rnorm(30, 8, 5))

child_function <- function(df, variable, hor.line = 6) {  
  variable <- enquo(variable)
  df <- df %>% mutate(mutation = 2 * !!variable, horizontal.line = hor.line)
}

parent_function <- function(df, date, variable, hor.line = 6) {
  date <- enquo(date)
  variable <- enquo(variable)
  df <- df %>% child_function(!!variable, hor.line) %>% View() # LINE 14
  p <- ggplot(df, aes(!!date, mutation)) + 
    geom_point() + 
    geom_hline(aes(yintercept = hor.line))
  p
}

parent_function(graph.data, date = cal.date, variable = random_num, hor.line = 8)

Answer 1

View() 是一个副作用函数，不会返回任何东西。

在您的第二种情况下，使用 magrittr 包中的 %T>% 而不是 %>%。

View() 结束管道，这样你就会想要一个 T pipe 代替。我想你可以像这样看得更清楚

 df %>% child_function(!!variable, hor.line) %>% View() -> df

对比

 df %>% child_function(!!variable, hor.line) %T>% View() -> df