r - 如何在 ggplot 之后使用 %T>% 管道？

Question

我们来看下面两段代码:

mtcars %>%
    ggplot(aes(x = cyl, y = mpg))+
    geom_line()

这有效并创建了以下情节:

现在让我们看看这个:

mtcars %>%
    group_by(cyl) %>% 
    summarise(mpg = mean(mpg))

这也有效并创建以下输出:

# A tibble: 3 x 2
    cyl   mpg
  <dbl> <dbl>
1     4  26.7
2     6  19.7
3     8  15.1

但是，这不起作用:

mtcars %T>%
    ggplot(aes(x = cyl, y = mpg))+
    geom_line() %>%
    group_by(cyl) %>% 
    summarise(mpg = mean(mpg))

它给出了以下错误:

Error in UseMethod("group_by") : 
  no applicable method for 'group_by' applied to an object of class "c('LayerInstance', 'Layer', 'ggproto', 'gg')"

为什么不起作用？从 %T>% 文档中，我希望左侧对象(在本例中为 mtcars)会在 ggplot 之后返回>。不幸的是，这似乎不起作用。我是否误解了 %T>% 管道？使这项工作正常运行的代码应该是什么样子？

Answer 1

您需要将 ggplot 调用包装在 print 中，以便同时调用。您可以使用以下代码:

library(tidyverse)
#> Warning: package 'ggplot2' was built under R version 4.1.2
#> Warning: package 'tibble' was built under R version 4.1.2
#> Warning: package 'tidyr' was built under R version 4.1.2
#> Warning: package 'readr' was built under R version 4.1.2
#> Warning: package 'dplyr' was built under R version 4.1.2
library(magrittr)
#> Warning: package 'magrittr' was built under R version 4.1.2
#> 
#> Attaching package: 'magrittr'
#> The following object is masked from 'package:purrr':
#> 
#>     set_names
#> The following object is masked from 'package:tidyr':
#> 
#>     extract
mtcars %T>%
  {print(ggplot(., aes(x = cyl, y = mpg))+
  geom_line())} %>%
  group_by(cyl) %>% 
  summarise(mpg = mean(mpg))

#> # A tibble: 3 × 2
#>     cyl   mpg
#>   <dbl> <dbl>
#> 1     4  26.7
#> 2     6  19.7
#> 3     8  15.1

^{由 reprex package 创建于 2022-06-30 (v2.0.1)}