ggplot分组折线图出现双图例，如何保留所需单个图例？

使用ggplot绘制分组折线图时出现两个图例，已调整其中一个为所需样式，但无法移除第二个，如何仅保留需要的图例？

原始代码 #

ggplot(data=data_Frame, aes(x=year, y=percent, group=legal, colour=as.factor(legal))) +
  geom_line(aes(linetype=as.factor(legal)))+
  geom_point()+
  geom_label_repel(aes(label = scales::percent(round(percent, digits=2))), nudge_x = 0.35, size = 3)+
  labs(y= "% of total cases", 
         x = "Year",
         title="Evolution of legal activity") +
  theme_classic()+
  scale_color_discrete(name = "Legality",
                        labels = c("Legal", "Not legal"))

数据集 #

structure(list(year = c(2013, 2014, 2014, 2015, 2015, 2016, 2016, 
2017, 2017, 2018, 2018, 2019, 2019, 2020, 2020, 2021, 2021, 2022, 
2022), legal = c(0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 
0, 1, 0, 1), local = c("yes", "yes", "yes", "yes", "yes", "yes", 
"yes", "yes", "yes", "yes", "yes", "yes", "yes", "yes", "yes", 
"yes", "yes", "yes", "yes"), percent = c(0.0833116184157648, 
0.134483022523174, 0.231061069599069, 0.0560278636136179, 0.272460808191276, 
0.10522051542274, 0.0823949547509575, 0.0902594024920258, 0.173996656575591, 
0.171213948427101, 0.331143680934122, 0.136188084988968, 0.219662510799276, 
0.0968133762744133, 0.216020359140314, 0.0929078672288155, 0.181961094549172, 
0.0871273239449852, 0.0913038796855186)), row.names = c(NA, -19L
), class = "data.frame")

出现两个图例的核心原因是同时使用了colour和linetype两个美学映射，它们各自生成独立图例。以下两种方法可解决问题：

方法一：合并图例（推荐） #

让线型图例与颜色图例合并，统一使用你设置的名称和标签，只需给scale_linetype_discrete设置相同参数：

ggplot(data=data_Frame, aes(x=year, y=percent, group=legal, colour=as.factor(legal))) +
  geom_line(aes(linetype=as.factor(legal)))+
  geom_point()+
  geom_label_repel(aes(label = scales::percent(round(percent, digits=2))), nudge_x = 0.35, size = 3)+
  labs(y= "% of total cases", 
         x = "Year",
         title="Evolution of legal activity") +
  theme_classic()+
  scale_color_discrete(name = "Legality",
                        labels = c("Legal", "Not legal")) +
  scale_linetype_discrete(name = "Legality",
                          labels = c("Legal", "Not legal"))

方法二：直接移除线型图例 #

若不需要通过线型区分分组，可通过guides()函数关闭线型图例：

ggplot(data=data_Frame, aes(x=year, y=percent, group=legal, colour=as.factor(legal))) +
  geom_line(aes(linetype=as.factor(legal)))+
  geom_point()+
  geom_label_repel(aes(label = scales::percent(round(percent, digits=2))), nudge_x = 0.35, size = 3)+
  labs(y= "% of total cases", 
         x = "Year",
         title="Evolution of legal activity") +
  theme_classic()+
  scale_color_discrete(name = "Legality",
                        labels = c("Legal", "Not legal")) +
  guides(linetype = "none")

额外优化建议 #

提前将legal列转换为因子，避免在映射中重复使用as.factor()，让代码更简洁：

data_Frame$legal <- factor(data_Frame$legal, levels = c(0,1), labels = c("Legal", "Not legal"))

ggplot(data=data_Frame, aes(x=year, y=percent, group=legal, colour=legal, linetype=legal)) +
  geom_line()+
  geom_point()+
  geom_label_repel(aes(label = scales::percent(round(percent, digits=2))), nudge_x = 0.35, size = 3)+
  labs(y= "% of total cases", 
         x = "Year",
         title="Evolution of legal activity") +
  theme_classic()+
  scale_color_discrete(name = "Legality") +
  scale_linetype_discrete(name = "Legality")

内容的提问来源于stack exchange，提问作者daviddupont