ggplot绘图：单变量三色展示仅保留一种图例项，移除NA图例

AI 小北

2026-6-28

问题需求

变量tei_tl需按规则显示黑、红、绿三种颜色：EU=1时为绿色，tei_tl<1时为红色，其余为黑色
图例仅保留tei_tl对应的黑色（标注为"TEI"）和Ann_av_te对应的蓝色（标注为"TEI annual averages"）
移除图例中无关的NA项

修改思路

将不需要生成图例的红、绿颜色直接通过geom的color参数（而非aes(color)）设置，避免这些颜色进入图例映射池
仅将需要在图例中展示的两个系列，通过aes(color)指定分组名称，确保图例只生成这两个项
用scale_color_manual精准绑定分组名称与对应颜色，同时设置图例标签

修改后的完整代码

# 加载依赖包
library(ggplot2)

# 导入用户提供的数据
datateff <- structure(list(Company = c("Ryanair", "Ryanair", "Ryanair", "Ryanair", 
"Ryanair", "Ryanair", "Ryanair", "Ryanair", "Ryanair", "Ryanair", 
"Singapore Airlines", "Singapore Airlines", "Singapore Airlines", "Singapore Airlines", "Singapore Airlines", "Singapore Airlines", 
"Singapore Airlines", "Singapore Airlines", "Singapore Airlines", "Singapore Airlines"), Year = c(2012, 2013, 2014, 2015, 2016, 
2017, 2018, 2019, 2020, 2021, 2012, 2013, 2014, 2015, 2016, 2017, 
2018, 2019, 2020, 2021), tei_tl = c(0.79265, 0.8301, 0.90591, 
0.89794, 0.92407, 0.91998, 1, 0.91571, 0.80457, 0.69001, 0.80559, 
0.80162, 0.79714, 0.76219, 0.75193, 0.81753, 0.83193, 0.79027, 
0.28713, 0.6495), EU = c(0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 0, 0, 0), Ann_av_te = c(0.77291, 0.80389, 0.83033, 
0.81141, 0.79951, 0.8164, 0.83807, 0.81942, 0.56056, 0.66667, 
0.77291, 0.80389, 0.83033, 0.81141, 0.79951, 0.8164, 0.83807, 
0.81942, 0.56056, 0.66667)), row.names = c(NA, -20L), class = c("tbl_df", 
"tbl", "data.frame"))

# 绘图代码
ggplot(data = datateff) + 
  # 绘制tei_tl线条：按条件设置颜色，不放入aes，不生成图例
  geom_line(aes(x = Year, y = tei_tl, group = Company),
            color = ifelse(datateff$EU == 1, "green", 
                           ifelse(datateff$tei_tl < 1, "red", "black"))) + 
  # 绘制tei_tl点：同样按条件设置颜色，不放入aes
  geom_point(aes(x = Year, y = tei_tl, group = Company),
             size = 1,
             color = ifelse(datateff$EU == 1, "green", 
                           ifelse(datateff$tei_tl < 1, "red", "black"))) + 
  # 绘制Ann_av_te线条：放入aes(color)指定图例名称
  geom_line(aes(x = Year, y = Ann_av_te, group = Company, color = "TEI annual averages")) + 
  # 添加透明线条仅用于生成TEI的图例项（实际不显示）
  geom_line(aes(x = Year, y = tei_tl, group = Company, color = "TEI"), alpha = 0) + 
  # 设置颜色映射：仅保留两个图例项，绑定对应颜色
  scale_color_manual(name = "", 
                     values = c("TEI" = "black", "TEI annual averages" = "#33CCFF"),
                     labels = c("TEI", "TEI annual averages")) + 
  labs(x = "Year", y = "") + 
  facet_wrap(~ Company, nrow = 5, ncol = 4) + 
  theme(axis.text = element_text(size = 6), 
        axis.title = element_text(size = 8), 
        text = element_text(size = 8), 
        legend.text = element_text(colour = "black", size = 6), 
        legend.title = element_text(colour = "black", size = 6), 
        legend.position = c(1.0, .01), 
        legend.justification = c("right", "bottom"), 
        legend.box.just = "right", 
        legend.margin = margin(6, 6, 6, 6))

代码说明

把tei_tl的线条和点的颜色从aes中移出，直接用ifelse条件赋值，红、绿颜色不会生成图例项
添加透明的geom_line仅用于在aes(color)中注册"TEI"分组，确保它出现在图例中，实际不会在图中显示
scale_color_manual只定义两个分组的颜色，自动过滤无关的NA项，最终图例仅显示黑色（TEI）和蓝色（TEI annual averages）

内容的提问来源于stack exchange，提问作者Montacer