Map colors 根据背景颜色在 ggplot 中添加标签

Question

如何改变 ggplot 中文本的颜色？ 例如，我有一个堆叠条形图 plot。我想在背景为浅蓝色或绿色时将标签设为黑色。

这是一个毫无意义的虚拟样本：

library(dplyr)
library(ggplot2)
df <- mpg %>% 
  mutate(cyl = as.character(cyl)) %>% 
  group_by(model, cyl) %>% 
  summarize(hwy = mean(hwy), .groups = "keep") %>% 
  ungroup() %>% 
  group_by(model) %>% 
  mutate(hwy = round(hwy / sum(hwy), 2)) %>% 
  ungroup() %>% 
  head(11) %>% 
  mutate(color = case_when(cyl == "4" ~ "white", 
                           cyl == "6" ~ "black", 
                           cyl == "8" ~ "black"))

df %>% 
  ggplot(data = ., aes(x = model, y = hwy, fill = cyl, label = hwy)) + 
  geom_bar(stat = "identity", position = "fill") + 
  geom_text(color = "white", position = position_stack(vjust = 0.5)) + 
  scale_fill_manual(values = c("dark blue", "light blue", "green"), 
                    name = "cyl",
                    breaks = c("4", "6", "8"),
                    labels = c("4", "6", "8"))

我尝试使用scale_color_manual ，如本例所示（ geom_text() 中有超过 1 种颜色），但它没有用。 这个例子中的解决方案甚至对我在问题本身的样本上都不起作用。 也许是因为它已经 8 岁了，idk。

在基于填充颜色的ggplot调用中动态选择 colors 的解决方案或将“颜色”变量映射到文本 colors 的解决方案都可以。

Answer 1

借用scales::show_col中的代码片段，根据填充 colors 的亮度将 label colors 设置为“黑色”或“白色”一个选项以实现您想要的结果可能如下所示：

library(dplyr)
library(ggplot2)
library(carver)

fill_colors <- c("dark blue", "light blue", "green")
# Borrowed from scales::show_col
hcl <- farver::decode_colour(fill_colors, "rgb", "hcl")
label_col <- ifelse(hcl[, "l"] > 50, "black", "white")

df %>% 
  ggplot(data = ., aes(x = model, y = hwy, fill = cyl, label = hwy)) + 
  geom_bar(stat = "identity", position = "fill") + 
  geom_text(aes(color = cyl), position = position_stack(vjust = 0.5), show.legend = FALSE) + 
  scale_fill_manual(values = fill_colors, 
                    name = "cyl",
                    breaks = c("4", "6", "8"),
                    labels = c("4", "6", "8")) +
  scale_color_manual(values = label_col)

Answer 2

因为你已经有了你想要的 colors，白色和黑色，在mutate语句中计算，map color = cyl （与fill美学相同）并添加具有所需值的scale_color_manual 。

df %>% 
  ggplot(aes(x = model, y = hwy, fill = cyl)) + 
  geom_bar(stat = "identity", position = "fill") + 
  geom_text(aes(color = cyl, label = hwy),
            position = position_stack(vjust = 0.5),
            show.legend = FALSE) + 
  scale_fill_manual(name = "cyl",
                    values = c("dark blue", "light blue", "green"), 
                    breaks = c("4", "6", "8"),
                    labels = c("4", "6", "8")) +
  scale_color_manual(values = c("white", "black", "black"),
                     breaks = c("4", "6", "8"))