'不能在顶层使用`!!!` 是什么意思。是什么意思以及如何解决？

Question

我正在尝试创建一个用于创建棒棒糖图的函数ggplot2。我想将所有参数传递...到aes()inside geom_point()。但是，我想排除size传递到aes()内部的参数geom_segment()（如果您查看a()下面的输出，原因很明显）。因此，我捕获...usingrlang::enquos()而不是按原样传递它。在功能上a()，我传递dots到aes()内ggplot()这个作品没有问题。但在功能上b()我得到了错误Can't use '!!!' at top level.

我被困在这一点上，并感谢任何输入来解决这个问题。

library(ggplot2)
data("mtcars")

d <- dplyr::count(mtcars, cyl, am)

a <- function(data, x, y, ...) {
  x <- rlang::enquo(x)
  y <- rlang::enquo(y)
  dots <- rlang::enquos(...)

  ggplot(data, aes(!!x, !!y, !!!dots)) +
    geom_segment(aes(y = 0, xend = !!x, yend = !!y)) +
    geom_point()
}

b <- function(data, x, y, ...) {
  x <- rlang::enquo(x)
  y <- rlang::enquo(y)

  dots <- rlang::enquos(...)
  segment_args <- dots[names(dots) != "size"]

  ggplot(data, aes(!!x, !!y)) +
    geom_segment(aes(y = 0, xend = !!x, yend = !!y, !!!segment_args)) +
    geom_point(aes(!!!dots))
}

a(d, cyl, n, color = factor(am), size = am)

b(d, cyl, n, color = factor(am), size = am)
#> Error: Can't use `!!!` at top level.

这是我的sessionInfo()：

R version 3.5.2 (2018-12-20)
Platform: x86_64-apple-darwin16.7.0 (64-bit)
Running under: macOS Sierra 10.12.1

Matrix products: default
BLAS: /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /usr/local/Cellar/openblas/0.3.5/lib/libopenblasp-r0.3.5.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods  
[7] base     

other attached packages:
[1] ggplot2_3.2.1

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.3       digest_0.6.18    withr_2.1.2     
 [4] assertthat_0.2.0 crayon_1.3.4     dplyr_0.8.3     
 [7] grid_3.5.2       R6_2.3.0         gtable_0.2.0    
[10] magrittr_1.5     scales_1.0.0     pillar_1.4.2    
[13] rlang_0.4.2      lazyeval_0.2.1   rstudioapi_0.10 
[16] labeling_0.3     tools_3.5.2      glue_1.3.0      
[19] purrr_0.3.3      munsell_0.5.0    compiler_3.5.2  
[22] pkgconfig_2.0.2  colorspace_1.4-0 tidyselect_0.2.5
[25] tibble_2.1.3

Answer 1

显然，这是一个已知问题，aes()您可以在此处验证。解决方法是这样的：

b <- function(data, x, y, ...) {
  x <- rlang::enquo(x)
  y <- rlang::enquo(y)

  dots <- rlang::enquos(...)
  segment_args <- dots[names(dots) != "size"]

  ggplot(data, aes(!!x, !!y)) +
    geom_segment(aes(, y = 0, xend = !!x, yend = !!y, !!!segment_args)) +
    geom_point(aes(, , !!!dots))
}

注意 中的单逗号geom_segment()和 中的双逗号geom_point()。