How to Add a Legend to Hline

How to add a legend to hline?

You can use the linetype aesthetic to make a separate legend for the horizontal lines rather than adding them to the existing legend.

To do this we can move linetype inside aes while still mapping to a constant. I used your desired labels as the constant. The legend name and the line type used can be set in scale_linetype_manual. I remove show.legend = TRUE to keep the lines out of the other legend. The legend colors are fixed in override.aes.

I + geom_hline(aes(yintercept= 10, linetype = "NRW limit"), colour= 'red') +
    geom_hline(aes(yintercept= 75.5, linetype = "Geochemical atlas limit"), colour= 'blue') +
    scale_linetype_manual(name = "limit", values = c(2, 2), 
                      guide = guide_legend(override.aes = list(color = c("blue", "red"))))

How to add the legend for hline in ggplot2

One option to achieve your desired result would be to map on aesthetics and make use of scale_xxx_manual instead of setting the color, linetypes, ... via arguments:

month=c("Jan","Feb","Mar","Apr","May","Jun")
rate=c(70,80,90,85,88,76) 
dd=data.frame(month,rate)
dd$type="Rate"
dd$month=factor(dd$month)

library(ggplot2)

ggplot(dd,aes(x=month,y=rate, color="Rate", linetype = "Rate")) + 
  geom_point(aes(x=month,y=rate, shape = "Rate"), size=2) +
  geom_text(aes(label = paste(format(rate, digits = 4, format = "f"), "%")), 
            color="black",vjust = -0.5, size = 3.5) +
  geom_line(aes(x = month, y = rate, group=1, size = "Rate")) + 
  geom_hline(aes(yintercept=85, color = "Target", linetype = "Target", size = "Target")) +
  labs(y = NULL, x= NULL, color = NULL, linetype = NULL, shape = NULL, size = NULL) + 
  scale_colour_manual(values = c(Rate = "#00BFC4", Target = "#F8766D")) +
  scale_linetype_manual(values = c(Rate = "solid", Target = "dashed")) +
  scale_shape_manual(values = c(Rate = 16, Target = NA)) +
  scale_size_manual(values = c(Rate = 1, Target = .5)) +
  theme(legend.position="bottom")

Add geom_hline to legend

Given solution works in most of the cases, but not for geom_hline (vline). For them you usually don't have to use aes, but when you need to generate a legend then you have to wrap them within aes:

library(ggplot2)
ggplot() +
  geom_line(aes(count, mean, color = "TrueMean"), myDf) +
  geom_hline(aes(yintercept = myTrueMean, color = "SampleMean")) +
  scale_colour_manual(values = c("red", "blue")) +
  labs(title = "Plot showing convergens of Mean",
       x = "Index",
       y = "Mean",
       color = NULL) +
  theme_minimal()

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Seeing original data you can use geom_point for better visualisation (also added some theme changes):

ggplot() +
  geom_point(aes(count, mean, color = "Observed"), myDf,
             alpha = 0.3, size = 0.7) +
  geom_hline(aes(yintercept = myTrueMean, color = "Expected"),
             linetype = 2, size = 0.5) +
  scale_colour_manual(values = c("blue", "red")) +
  labs(title = "Plot showing convergens of Mean",
       x = "Index",
       y = "Mean",
       color = "Mean type") +
  theme_minimal() +
  guides(color = guide_legend(override.aes = list(
    linetype = 0, size = 4, shape = 15, alpha = 1))
  )

How can I add legend to multiple hlines in ggplot2?

To show a legend in a ggplot, you should create an aesthetic mapping. The simplest way to do that is to have a seperate little data frame that contains the information you want to show on your hlines.

You haven't provided any sample data, so I've made some up here so that this is a fully reproducible example:

library(ggplot2)

set.seed(69)
main_data <- data.frame(x = rnorm(200, 10), y = rnorm(200, 10))
hline_data <- data.frame(y = c(8, 10, 12), type = factor(c(2, 1, 2)), 
                         stringsAsFactors = FALSE)

ggplot(main_data, aes(x,y)) + 
  geom_point() + 
  geom_hline(data = hline_data, 
             aes(yintercept = y, linetype = type, colour = type)) +
  scale_colour_manual(values = c("blue", "red"), 
                      labels = c("Recommended Spacing", "Limits of spacing"),
                      name = "Key") +
  scale_linetype_manual(values = 1:2, 
                        labels = c("Recommended Spacing", "Limits of spacing"),
                        name = "Key")

^{Created on 2020-05-19 by the reprex package (v0.3.0)}

how to add and edit a legend in goem_hline() in R

Update: OP request:

p <- ggplot(data=df, aes(x=year_date, y=total, fill=name))+ 
  geom_col(position = "dodge")+
  scale_fill_manual(values=c("#08088A","#9F81F7"))+
  theme_light()+labs(fill="rain", title ="rain anual", x="Estation", y="total mm")+
  theme(axis.text.x = element_text(angle = 90)) 

data_line <- data.frame(yintercept=18, data_line=factor(18))

p + 
  geom_hline(data=data_line, aes(yintercept=yintercept, linetype="18"), size=1.5, col="#ffff00") +
  scale_linetype_manual(name = "Historiacal serie",values = c(1,1)) 

Add geom_hline legend to existing geom bar legend

As @Gregor suggested, you could use a direct label for this line by adding annotate() as shown below:

ggplot(df, aes(x=Outcome2, y=d, fill=study)) + 
   geom_bar(position=position_dodge(), aes(x=Outcome2),stat="identity",
             colour="black", # Use black outlines,
             size=.3) +      # Thinner lines
    xlab("Outcome") +
    ylab("Cohen's D Effect Size") +
    scale_fill_grey(name="Study", 
                   labels=c("study1","study2", "study3"))+
        theme_bw()+
    geom_hline(yintercept=.15,linetype=2) +annotate("text",x=.7,y=.17,size=3,label=c('avg tx ef')) 

If space is an issue you can use the wrapper described here to wrap the text. Just run wrapper <- function(x, ...) paste(strwrap(x, ...), collapse = "\n") then add +annotate("text",x=.7,y=.18,size=3,label=wrapper('avg tx effect',10)). Which produces:

Add axhline to legend

Simply using plt.legend() tells you what data is being plotting:

You are using someBoolean as the hue. So you are essentially creating two lines by applying a Boolean mask to your data. One line is for values that are False (shown as 0 on the legend above), the other for values that are True (shown as 1 on the legend above).

In order to get the legend you want you need to set the handles and the labels. You can get a list of them using ax.get_legend_handles_labels(). Then make sure to omit the first handle which, as shown above, has no artist:

ax = sns.lineplot(x="x", y="y", hue="someBoolean", data=data)

plt.axhline(y=7, c='red', linestyle='dashed', label="horizontal")

labels = ["some name", "some other name", "horizontal"]
handles, _ = ax.get_legend_handles_labels()

# Slice list to remove first handle
plt.legend(handles = handles[1:], labels = labels)

This gives:

How to add a custom legend for geom_hline

It's a bit awkward, but this 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've included legend.title = element_blank() in there, which is why the legend is not named. Remove that to include the name.

In ggplot2, how to display a legend using geom_hline function?

geom_hline is special: its show_guide argument is FALSE by default, in contrast to most other geoms (presumably because geom_hline is so often used for annotation ...)

You didn't give a reproducible example before I initially answered the question, but this slightly hacked example seems to work:

library(ggplot2)
 p <- ggplot(mtcars, aes(x = wt, y=mpg)) + geom_point()
p + geom_hline(aes(lty="foo",yintercept=20),show_guide=TRUE)+
   scale_linetype_manual(name="",values=2)

The ugliness is because there needs to be something to show in the guide (legend); just saying geom_hline(yintercept=20,lty=2,show_guide=TRUE) doesn't work. There's probably a more principled way to do this, though.

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