如何在 ggplot 的条形图中添加阴影、条纹或其他图案或纹理？

Question

假设我有一个包含序数变量和分类变量的数据：

set.seed(35)
df <- data.frame(Class = factor(rep(c(1,2),times = 80), labels = c("Math","Science")),
                 StudyTime = factor(sort(sample(1:4, 16, prob = c(0.25,0.3,0.3,0.15), replace = TRUE)),labels = c("<5","5-10","10-20",">20")),
                 Nerd = factor(sapply(rep(c(0.1,0.3,0.5,0.8),c(30,50,50,30)), function(x)sample(c("Nerd","NotNerd"),size = 1, prob = c(x,1-x))),levels = c("NotNerd","Nerd")))

可以使用ggplot 和geom_bar 与x、fill 和alpha（或color）美学映射来可视化这些变量之间的关系。

ggplot(data = df, aes(x = Class, fill = StudyTime, alpha = Nerd)) + 
  geom_bar(position = "dodge", color = "black") + 
  scale_alpha_manual(values = c(Nerd = 0.5, NotNerd = 1)) +
  scale_fill_manual(values = colorRampPalette(c("#0066CC","#FFFFFF","#FF8C00"))(4)) +
  labs(x = "Class", y = "Number of Students", alpha = "Nerd?") +
  theme(legend.key.height = unit(1, "cm"))

但是，alpha 和 color 并不理想。更好的选择可能是应用条纹或交叉影线等图案。

10 多年前对this question 的公认答案是使用颜色，而the most upvoted answer（虽然聪明）使用超过 100 行代码。

This question 收到了一些赞成票，但没有新的答案。

有没有更好的选择来添加一个模式，比如可以在这里看到？

Answer 1

一种方法是使用 Mike FC（无从属关系）编写的 ggpattern 包：

library(ggplot2)
#remotes::install_github("coolbutuseless/ggpattern")
library(ggpattern)
ggplot(data = df, aes(x = Class, fill = StudyTime, pattern = Nerd)) +
  geom_bar_pattern(position = position_dodge(preserve = "single"),
                   color = "black", 
                   pattern_fill = "black",
                   pattern_angle = 45,
                   pattern_density = 0.1,
                   pattern_spacing = 0.025,
                   pattern_key_scale_factor = 0.6) + 
  scale_fill_manual(values = colorRampPalette(c("#0066CC","#FFFFFF","#FF8C00"))(4)) +
  scale_pattern_manual(values = c(Nerd = "stripe", NotNerd = "none")) +
  labs(x = "Class", y = "Number of Students", pattern = "Nerd?") + 
  guides(pattern = guide_legend(override.aes = list(fill = "white")),
         fill = guide_legend(override.aes = list(pattern = "none")))

该软件包似乎支持许多常见的几何形状。以下是使用geom_tile 将连续变量与分类变量组合的示例：

set.seed(40)
df2 <- data.frame(Row = rep(1:9,times=9), Column = rep(1:9,each=9),
                   Evaporation = runif(81,50,100),
                   TreeCover = sample(c("Yes", "No"), 81, prob = c(0.3,0.7), replace = TRUE))

ggplot(data=df2, aes(x=as.factor(Row), y=as.factor(Column),
                     pattern = TreeCover, fill= Evaporation)) +
  geom_tile_pattern(pattern_color = NA,
                    pattern_fill = "black",
                    pattern_angle = 45,
                    pattern_density = 0.5,
                    pattern_spacing = 0.025,
                    pattern_key_scale_factor = 1) +
  scale_pattern_manual(values = c(Yes = "circle", No = "none")) +
  scale_fill_gradient(low="#0066CC", high="#FF8C00") +
  coord_equal() + 
  labs(x = "Row",y = "Column") + 
  guides(pattern = guide_legend(override.aes = list(fill = "white")))