How to add custom legend for geom_hline

Question

Using the data below, note that the legend does not describe geom_hline:

df<-data.frame( points=c(.153,.144,.126,.035, .037, .039, .010,.015,.07), days=gl(3,1,9,labels=c("Sun","Mon","Tues")), lang=c("en","en","en","pt","pt","pt","ko","ko","ko")) ggplot(data=df[df$lang=="en",])+ geom_point(aes(x=days,y=points),size=5,colour='cyan',show_guide=F)+ geom_point(aes(x=days,y=points,colour=days),size=4,show_guide=F)+ facet_wrap(~lang,ncol=1,scales="free")+ xlab("")+ ylab("")+ scale_y_continuous(labels = percent_format())+ theme(legend.position="right", legend.title = element_blank(), strip.text.x = element_text(size = 13, colour = 'black', angle = 0), axis.text.x=element_text(angle=0, hjust=.5, vjust=0), legend.position = 'none', panel.background = element_rect(fill = "#545454"), panel.grid.major = element_line(colour = "#757575"), panel.grid.minor = element_line(colour = "#757575"))+ geom_hline(yintercept=.136,color='cyan',size=2, show_guide=T) 

Is there a way to create a custom legend describing geom_hline? [I would like the legend to have the name "Legend" with only one meaning of "avg"]

Searching so, I found an example: the ggplot legend showing transparency and fill color . They used the scale_fill_manual, which I tried, but could not improve the legend shown above.

Answer 1

This is a bit uncomfortable, but it seems to work:

 hline <- data.frame(yint = 0.136,lt = 'Avg') ggplot(data=df[df$lang=="en",])+ geom_point(aes(x=days,y=points),size=5,colour='cyan')+ geom_point(aes(x=days,y=points,colour=days),size=4)+ facet_wrap(~lang,ncol=1,scales="free")+ xlab("")+ ylab("")+ scale_y_continuous(labels = percent_format())+ theme(legend.position="right", legend.title = element_blank(), strip.text.x = element_text(size = 13, colour = 'black', angle = 0), axis.text.x=element_text(angle=0, hjust=.5, vjust=0), legend.position = 'none', panel.background = element_rect(fill = "#545454"), panel.grid.major = element_line(colour = "#757575"), panel.grid.minor = element_line(colour = "#757575"))+ geom_hline(data = hline,aes(yintercept=yint,linetype = lt),color = "cyan",size=2,show_guide = TRUE) + scale_colour_discrete(guide = "none") + scale_linetype_manual(name = 'Legend',values = 1,guide = "legend") 

Ah, but you included legend.title = element_blank() there, so the legend is not named. Remove this to include the name.