如何合并ggpattern与ggplot2图例：整合条纹到颜色图例

问题场景 #

制作世界地图时，用颜色区分国家分组，为适配黑白打印给其中一组添加条纹图案，但当前ggplot2的颜色图例和ggpattern的图案图例是分开的，需要将条纹整合到颜色图例中，移除独立的图案图例。

原始代码 #

library(tidyverse)
library(ggplot2)
library(ggpattern)

breaks <- c(-Inf, 0, Inf)
labels <- c("negative", "positive")
world_map <- map_data(map = "world")
data <- data.frame(country_map = unique(world_map$region))
data$mean <- -1
data$mean[data$country_map == "Russia"] <- 1
data$group <- cut(data$mean, breaks = breaks, labels = labels)
data$pattern <- ifelse(data$mean < 0, "stripe", NA)

ggplot(data) + geom_map(aes(map_id = country_map, fill = fct_rev(group)), map = world_map) + #coord_proj("+proj=robin", xlim = c(-135, 178.5), ylim = c(-56, 84)) + 
  geom_polygon(data = world_map, aes(x = long, y = lat, group = group), colour = 'grey', size = 0,  fill = NA) + expand_limits(x = world_map$long, y = world_map$lat) + theme_void() + 
  geom_map_pattern(data = data, map = world_map, aes(map_id = country_map, pattern = pattern), pattern_fill = "black", fill = NA, pattern_density = 0.1, pattern_angle = 30, pattern_spacing = 0.02) #+
  #scale_fill_manual(name = "Group", drop = FALSE, values = c("red", "blue"), labels = labels)

解决方案 #

核心思路是让fill和pattern映射到同一个分组变量，通过手动刻度和图例引导来合并两者的图例。修改后的代码如下：

library(tidyverse)
library(ggplot2)
library(ggpattern)

breaks <- c(-Inf, 0, Inf)
labels <- c("negative", "positive")
world_map <- map_data(map = "world")
data <- data.frame(country_map = unique(world_map$region))
data$mean <- -1
data$mean[data$country_map == "Russia"] <- 1
data$group <- cut(data$mean, breaks = breaks, labels = labels)

ggplot(data) +
  # 基础颜色填充层
  geom_map(aes(map_id = country_map, fill = group), map = world_map) +
  # 地图边界层
  geom_polygon(data = world_map, aes(x = long, y = lat, group = group), 
               colour = 'grey', size = 0, fill = NA) +
  # 图案填充层，将pattern映射到group
  geom_map_pattern(aes(map_id = country_map, pattern = group), 
                   map = world_map,
                   pattern_fill = "black", fill = NA,
                   pattern_density = 0.1, pattern_angle = 30, pattern_spacing = 0.02) +
  # 手动指定颜色刻度
  scale_fill_manual(name = "Group", 
                    values = c("negative" = "red", "positive" = "blue"),
                    labels = labels) +
  # 手动指定图案刻度，不需要图案的组设为NA
  scale_pattern_manual(name = "Group",
                       values = c("negative" = "stripe", "positive" = NA),
                       labels = labels) +
  # 合并图例，让fill和pattern共用一个，移除多余的图案图例
  guides(pattern = guide_legend(override.aes = list(fill = c("red", "blue"))),
         fill = guide_legend(override.aes = list(pattern = c("stripe", NA)))) +
  expand_limits(x = world_map$long, y = world_map$lat) +
  theme_void()

关键改动说明 #

• 移除单独的pattern列，将pattern直接映射到group变量，让颜色和图案绑定到同一分组
• 使用scale_pattern_manual为需要添加条纹的分组指定stripe，另一组设为NA
• 通过guides参数，让fill和pattern的图例合并，互相覆盖对方的美学参数，确保图例项同时显示颜色和对应的图案
• 统一图例名称为"Group"，避免出现两个独立图例

内容的提问来源于stack exchange，提问作者bixiou