如何将自定义图例添加到绘图R

Question

因此，我正在尝试向R图添加自定义图例。我正在尝试添加此图例，以说明我的情节中的线条：

因此，我的目标是要有一个传说，说蓝线代表标准偏差。

到目前为止，这是我的代码：

kernal.dens <- ggplot(daily.ret2.df, aes(x=Daily,color = year))+
  geom_density(data = filter(daily.ret2.df, year != 2019),adjust=2, size=1, show.legend = T)+
  geom_density(data = daily.ret2.12,adjust=2, size=1.75, show.legend = T)+
  geom_segment(lty=1,aes(x = sd(daily.ret2.12$Daily),xend = sd(daily.ret2.12$Daily),
                         yend = 5,y = 0),color = "blue",size = .5)+
  geom_segment(lty=1,aes(x = sd(daily.ret2.12$Daily)*2,xend = sd(daily.ret2.12$Daily)*2,
                         yend = 5,y = 0),color = "blue",size = .5)+
  geom_segment(lty=1,aes(x = sd(daily.ret2.12$Daily)*-1,xend = sd(daily.ret2.12$Daily)*-1,
                         yend = 5,y = 0),color = "blue",size = .5)+
  geom_segment(lty=1,aes(x = sd(daily.ret2.12$Daily)*-2,xend = sd(daily.ret2.12$Daily)*-2,
                         yend = 5,y = 0),color = "blue",size = .5)+
  scale_color_manual(values=c( "black", '#3A8026', "#7F8931", "#C4933D","#C47422", "#C45608", 
                              "#B12F08", "#9E0808", "#80262D"),
                     labels = c(' Last 12 Months ',' 2011   ',' 2012   ',' 2013   ',' 2014   ',' 2015   ',' 2016   ',
                                ' 2017   ',' 2018   '))+
 legendGrob(labels = 'Sd',do.lines = T,nrow = 1,ncol = 1)+
  grid.legend(draw = T)+
  scale_x_continuous(breaks = seq(-.1,.1,.05), 
                     labels = paste0(seq(-.1,.1,.05)*100,'%'))+
  scale_y_continuous(breaks = seq(0,50,5))+
  labs(x='\nReturn\n',y='Density\n',title=paste0(asset, ' Daily Return Densities\n'))+
  theme(plot.title=element_text(hjust=.5,size=44-max(0,nchar(asset)-6),face='bold'),
        axis.text=element_text(size=20,color='black',face='bold'),
        axis.title=element_text(size=28,color='black',face='bold'),
        legend.text=element_text(size=18,color='black',face='bold'),
        legend.title=element_blank(),
        legend.position = 'bottom',
        plot.margin=unit(c(1,1,1,1),"cm"))

当我把它放进去时，我得到这个错误：

Error: Don't know how to add legendGrob(labels = "Sd", do.lines = T, nrow = 1, ncol = 1) to a plot

我认为错误是R没有数据知道图例中每个项目对应的情节。

每当我看到一个添加自定义绘图的示例时，已经有一个旧绘图要替换，但是就我的情况而言，我想要一个不存在的绘图。

感谢您的时间，无论您有什么能力帮助我。我也很乐意在R和相关主题中添加图例以进一步了解它们的任何建议。