ggplot2双轴图图例格式设置：合并图例并删除冗余项

问题需求 #

• 将两个独立图例合并为一个统一图例
• 删除图例中多余的Overall Balance (N$ Million)条目（仅保留柱状图对应类别和Overall Balance (% of GDP, RHS)）

修改后的完整代码 #

dat <- structure(list(Category = c("Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)", 
"Deficit Target (% of GDP, RHS)", "Overall Balance (N$ Million)", 
"Overall Balance (% of GDP, RHS)", "Deficit Target (% of GDP, RHS)", 
"Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)", 
"Deficit Target (% of GDP, RHS)", "Overall Balance (N$ Million)", 
"Overall Balance (% of GDP, RHS)", "Deficit Target (% of GDP, RHS)", 
"Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)", 
"Deficit Target (% of GDP, RHS)", "Overall Balance (N$ Million)", 
"Overall Balance (% of GDP, RHS)", "Deficit Target (% of GDP, RHS)", 
"Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)", 
"Deficit Target (% of GDP, RHS)"), Year = c("2018/19", "2018/19", 
"2018/19", "2019/20", "2019/20", "2019/20", "2020/21", "2020/21", 
"2020/21", "2021/22 (est)", "2021/22 (est)", "2021/22 (est)", 
"2022/23 (proj)", "2022/23 (proj)", "2022/23 (proj)", "2023/24 (proj)", 
"2023/24 (proj)", "2023/24 (proj)", "2024/25 (proj)", "2024/25 (proj)", 
"2024/25 (proj)"), Value = c(-9226, -5.09893041491584, -3, -8918, 
-4.97862890962981, -3, -14197, -8.04324429255841, -3, -16138, 
-8.8, -3, -12658, -6.5, -3, -10418, -5, -3, -10281, -4.7, -3)), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -21L))

library(tidyverse)

ggplot() +
  # 柱状图仅保留fill映射，移除多余的color映射
  geom_col(data = subset(dat, Category == "Overall Balance (N$ Million)"),
           mapping = aes(x = Year, y = Value, fill = Category),
           position = position_dodge()) +
  # 折线图保留color映射
  geom_line(data = subset(dat, Category == "Overall Balance (% of GDP, RHS)"),
            mapping = aes(x = Year, y = (Value*1500), color = Category), 
            size = 2) +
  # 配置fill图例：指定颜色、保留需要的类别，自定义图例样式实现合并
  scale_fill_manual(
    values = c("Overall Balance (N$ Million)" = '#7c3042'),
    limits = c("Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)"),
    guide = guide_legend(override.aes = list(
      fill = c('#7c3042', NA),
      color = c(NA, '#c7af76'),
      shape = c(22, NA),
      linetype = c(0, 1)
    ))
  ) +
  # 配置color映射：指定颜色、匹配limits，关闭单独图例
  scale_color_manual(
    values = c("Overall Balance (% of GDP, RHS)" = '#c7af76'),
    limits = c("Overall Balance (N$ Million)", "Overall Balance (% of GDP, RHS)"),
    guide = "none"
  ) +
  theme_light() +
  labs(x = '') +
  scale_y_continuous(
    breaks = seq(-22000,3000,by = 5000),
    name = 'Overall Balance (N$ Million)',
    sec.axis= sec_axis(~./1500, name="Overall Balance (% of GDP)", breaks = seq(-10,0, by = 2))
  ) +
  theme(legend.title = element_blank())

关键改动说明 #

• 移除柱状图的color映射：原代码中柱状图同时设置fill和color，导致生成两个独立图例，移除后仅通过fill区分柱状图，减少图例来源。
• 合并图例配置：在scale_fill_manual中通过limits指定需要保留的两个类别，再用guide_legend(override.aes)自定义每个图例条目的显示样式：柱状图对应填充色块、无线条，折线图对应线条、无填充，实现两个类别合并到同一图例。
• 关闭color的单独图例：在scale_color_manual中设置guide = "none"，避免生成第二个独立图例，同时用键值对形式指定颜色与类别的对应关系，确保样式准确。

内容的提问来源于stack exchange，提问作者Tanga94