使用ggplot绘图调用scale_*_manual后图例仍不显示问题求助

问题根因 #

• 你在geom_line()、geom_point()的aes()内部声明了color映射后，又在函数外部重复指定了固定color值，这会直接覆盖映射逻辑，ggplot不会为硬编码的美学属性生成图例。
• 你所有分组用的是color美学，但最后调用的是scale_fill_discrete()，fill针对的是填充类元素（如柱状图的柱身），和你使用的线条、点的color属性完全不对应，无法生效。
• 你在aes中传入的color值是色号，不是菌株类别名称，就算生成图例也会显示色号而非你需要的菌株名。

修正代码 #

最小改动版本（无需修改数据结构） #

ggplot(data = OD)+
  theme_light()+
  # 去掉geom外部的硬编码color，aes内color传入菌株名
  geom_line(aes(x=Days, y=Wildtype, group=1, color="Wildtype"), linetype="solid")+
  geom_point(aes(x=Days, y=Wildtype, group=1, color="Wildtype"), shape=15, size=1.5)+
  geom_errorbar(aes(x=Days, y=Wildtype, ymin=Wildtype-SD, ymax=Wildtype+SD),width=.2, position=position_dodge(0.05))+
  geom_line(aes(x=Days, y=Winter, group=1, color="Winter"), linetype="solid")+
  geom_point(aes(x=Days, y=Winter, group=1, color="Winter"), shape=15, size=1.5)+
  geom_errorbar(aes(x=Days, y=Winter, ymin=Winter-SD.1, ymax=Winter+SD.1),width=.2, position=position_dodge(0.05))+
  geom_line(aes(x=Days, y=Flagella_less, group=1, color="Flagella_less"), linetype="solid")+
  geom_point(aes(x=Days, y=Flagella_less, group=1, color="Flagella_less"), shape=15, size=1.5)+
  geom_errorbar(aes(x=Days, y=Flagella_less, ymin=Flagella_less-SD.2, ymax=Flagella_less+SD.2),width=.2, position=position_dodge(0.05))+
  labs(title="Growth curve",x="Days",y="OD750",color="菌株")+
  theme(axis.text.x=element_text(angle=90,hjust=1,vjust=0.5,color="black",size=8),
        axis.text.y=element_text(angle=0,hjust=1,vjust=0.5,color="black",size=8),
        plot.title=element_text(hjust=0.5, size=12,face = "bold",margin = margin(t=0, r=10,b=10,l=10)),
        axis.title.y =element_text(size=10, margin=margin(t=0,r=10,b=0,l=0)),
        axis.title.x =element_text(size=10, margin=margin(t=10,r=10,b=0,l=0)),
        legend.position = "right")+
  # 替换为color对应的标度，手动指定颜色
  scale_color_manual(values = c("Wildtype" = "darkorange2",
                                "Winter" = "cadetblue3",
                                "Flagella_less" = "olivedrab3"))

更规范的版本（先转长格式数据，代码更简洁易维护） #

library(tidyr)
library(dplyr)

# 宽数据转长数据
OD_long <- OD %>%
  select(Days, Wildtype, Winter, Flagella_less, SD, SD.1, SD.2) %>%
  pivot_longer(cols = c(Wildtype, Winter, Flagella_less),
               names_to = "Strain",
               values_to = "OD_value") %>%
  mutate(SD_value = case_when(
    Strain == "Wildtype" ~ SD,
    Strain == "Winter" ~ SD.1,
    Strain == "Flagella_less" ~ SD.2
  ))

# 绘图代码
ggplot(OD_long, aes(x = Days, y = OD_value, color = Strain, group = Strain)) +
  theme_light() +
  geom_line(linetype = "solid") +
  geom_point(shape = 15, size = 1.5) +
  geom_errorbar(aes(ymin = OD_value - SD_value, ymax = OD_value + SD_value),
                width = 0.2, position = position_dodge(0.05)) +
  labs(title = "Growth curve", x = "Days", y = "OD750", color = "菌株") +
  theme(axis.text.x=element_text(angle=90,hjust=1,vjust=0.5,color="black",size=8),
        axis.text.y=element_text(angle=0,hjust=1,vjust=0.5,color="black",size=8),
        plot.title=element_text(hjust=0.5, size=12,face = "bold",margin = margin(t=0, r=10,b=10,l=10)),
        axis.title.y =element_text(size=10, margin=margin(t=0,r=10,b=0,l=0)),
        axis.title.x =element_text(size=10, margin=margin(t=10,r=10,b=0,l=0)),
        legend.position = "right") +
  scale_color_manual(values = c("Wildtype" = "darkorange2",
                                "Winter" = "cadetblue3",
                                "Flagella_less" = "olivedrab3"))

内容的提问来源于stack exchange，提问作者paula