如何使用R和ggplot修改线条颜色？代码颜色不生效问题求助

你把颜色参数color = "blue"/color = "orange"放在了aes()内部，此时ggplot会把这些字符串当成分类变量的取值，而非直接应用的颜色值，所以它会调用默认离散色板给这两个“类别”上色，而非你指定的蓝、橙。

方法一：直接在geom_line外设置颜色（简单场景） #

把颜色参数从aes()中移出，作为geom_line的独立参数，直接指定颜色：

q <- ggplot(data = graph_data, aes(x = Year_NA)) +    
  geom_line(aes(y = MTCT_rate_at_before_birth_mean), color = "blue") +
  geom_line(aes(y = Postnatal_MTCT_rate_to_18_months_from_HIV_diagnosed_mothers_mean), color = "orange") +
  labs(title = "MTCT rate postnatal vs. prenatal Vs. Year",  
       y = "MTCT Rate", x = "Year") + 
  theme_bw() 
show(q)

方法二：用scale_color_manual映射自定义颜色（规范场景） #

如果需要保留图例并自定义颜色，建议在aes()中使用语义化的分类标签，再通过scale_color_manual将标签映射到对应颜色：

q <- ggplot(data = graph_data, aes(x = Year_NA)) +    
  geom_line(aes(y = MTCT_rate_at_before_birth_mean, color = "MTC before birth")) +
  geom_line(aes(y = Postnatal_MTCT_rate_to_18_months_from_HIV_diagnosed_mothers_mean, color = "MTCT after birth")) +
  labs(title = "MTCT rate postnatal vs. prenatal Vs. Year",  
       y = "MTCT Rate", x = "Year",
       color = "") +
  scale_color_manual(values = c("MTC before birth" = "blue", "MTCT after birth" = "orange")) +
  theme_bw() 
show(q)

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