如何为ggplot2中重叠的geom_rect添加额外图例项

要在现有图例里加入红蓝透明重叠后的颜色条目，只需两步操作：

1. 生成重叠区域的对应颜色 #

红（alpha=0.1）和蓝（alpha=0.1）重叠后会呈现品红色，其alpha值可通过透明色叠加公式计算：1 - (1-0.1)*(1-0.1) = 0.19，用rgb()函数直接生成该颜色：

overlap_color <- rgb(1, 0, 1, alpha = 0.19)

2. 修改颜色映射参数 #

在scale_fill_manual里加入第三个颜色条目，同时用breaks参数强制显示所有三个图例项：

完整代码 #

# library
library(ggplot2)
library(tidyverse)

# 生成透明颜色及重叠色
adjustcolor("red", alpha.f = 0.1) -> red.tra
adjustcolor("blue", alpha.f = 0.1) -> blue.tra
overlap_color <- rgb(1, 0, 1, alpha = 0.19)

# 数据
data <-  structure(list(unclear = c(0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 
                                    1), start = structure(c(12784, 13879, 9496, 17897, 11323, 12053, 
                                                            16801, 16071, 17167, 17532, 16071, 11323, 11688), class = "Date"), 
                        stop = structure(c(18628, 18628, 16801, 18262, 13879, 17897, 
                                           18262, 17897, 17532, 18628, 17897, 18262, 11688), class = "Date"), 
                        group = c("R", "C", "C", "A", "A", "R", "M", "N", 
                                            "N", "O", "OB", "H", "H")), class = "data.frame", row.names = c(NA, 
                                                                                                            -13L))

# 绘图
ggplot(data = data)+
  geom_rect(data = data %>% filter(unclear==0), aes(xmin=start, xmax=stop, ymin=0, ymax=0.7, fill="one")) +
  geom_rect(data = data %>% filter(unclear==1), aes(xmin=start, xmax=stop, ymin=0, ymax=0.7, fill="two"))+
  scale_fill_manual(
    name = "colors",
    values = c(one = red.tra, two = blue.tra, overlap = overlap_color),
    labels = c("one", "two", "重叠区域"),
    breaks = c("one", "two", "overlap") # 强制显示所有三个图例条目
  )+
  facet_wrap(~group, ncol = 1, strip.position = "left") 

关键说明 #

• breaks参数用于指定图例要显示的所有键，即使第三个键没有被任何图层直接调用，也会在图例中正常呈现。
• 重叠颜色的alpha值是严格按照透明色叠加规则计算的，确保和实际图层重叠后的视觉效果一致。

内容的提问来源于stack exchange，提问作者ava