为Hline ggplot2添加图例标签

Question

我正在尝试根据添加的一些水平比较行向ggplot2添加图例。我的代码目前看起来像这样

aplot <- ggplot(aData, aes(x = DEP, y = DECAY, color = GENDER))        
aplot + 
  geom_point() +
  geom_smooth(method = "lm", se = FALSE) +
  geom_hline(yintercept = meanCD, color = "purple")+
  geom_hline(yintercept = medianCD, color = "forestgreen") +
  geom_hline(yintercept = medianSAD, color = "goldenrod3", linetype = "dashed")+
  geom_hline(yintercept = meanSAD, color = "deeppink", linetype = "dashed") 

meanCD，medianCD，meanSD，medianSD都存储为单独的值，我需要将它们添加到图表中以进行比较。 aData只是一堆点。我不能得到一个图例来显示线条的颜色并给出一个合适的标签，我不确定如何在ggplot2中完成此任务。