向 geom_bar() / geom_col() 条添加图案或纹理？

有时，我需要某种用于 geom_bar() / geom_col() 条的图案或纹理（即用于黑白打印）。例如，以下内容对于某些人来说可能很难查看：

library(ggplot2)
library(dplyr, warn.conflicts=FALSE)
library(tidyr)

d <- iris %>% 
    group_by(Species) %>% 
    summarize_all(mean) %>% 
    gather(key, val, -Species)

ggplot(d, aes(x = Species, y = val, fill = key)) +
    geom_col(position = "dodge") +
    scale_fill_grey()

曾经有过Stack Overflow 上的好问题和答案 https://stackoverflow.com/questions/2895319/how-to-add-texture-to-fill-colors-in-ggplot2 (also ）。然而，解决方案很复杂，并且基本上涉及手工创建图案或纹理。我想知道是否有人有一般想法或建议或新方法以不同的方式解决这个问题。通常，当我认为我不能用 ggplot2 做某事时，这意味着改变我对解决它的想法 - 但其他（罕见）时间它只是还没有实现！

您可以使用添加模式ggpattern package https://coolbutuseless.github.io/2020/04/01/introducing-ggpattern-pattern-fills-for-ggplot/

# remotes::install_github("coolbutuseless/ggpattern")
library(ggpattern)
library(ggplot2)
library(dplyr, warn.conflicts=FALSE)
library(tidyr)
  
  d <- iris %>% 
    group_by(Species) %>% 
    summarize_all(mean) %>% 
    gather(key, val, -Species)
  
  ggplot(d, aes(x = Species, y = val, fill = key)) +
    geom_col_pattern(position = "dodge",
             pattern = 
               c(
                 "stripe", "stripe", "stripe", # 3rd col
                 "stripe", "stripe", "stripe", # 4th col
                 "none", "none", "none", # 1st col
                 "crosshatch", "crosshatch", "crosshatch" # 2nd col
             ),
             pattern_angle = c(rep(0, 3), 
                               rep(45, 3), 
                               rep(0, 6)),
             pattern_density = .1,
             pattern_spacing = .04,
             pattern_fill = 'black') +
    scale_fill_grey() +
  guides(fill = guide_legend(override.aes = 
                               list(
                                 pattern = c("none", "crosshatch", "stripe", "stripe"),
                                 pattern_spacing = .01,
                                 pattern_angle = c(0, 0, 0, 45)
                                 )
                             ))

^{Created on 2021-01-13 by the reprex package https://reprex.tidyverse.org (v0.3.0)}