how to add dashed horizontal line with label in ggplot

Question

I have plotted a line plot. I have added a horizontal line on the plot. How to take horizontal line red dashed?

# Sample Data 

library(tidyverse)
Month= c("Jan","Feb","Mar","Apr","May","Jun")
a = c(11,10,9,8,4,8)

test= data_frame(Month,a) 
test$cum_total <- cumsum(test$a)

test$Month <- factor(test$Month, month.abb)

# ggplot

ggplot(data=test, aes(x=Month, y=cum_total, group=1)) +
  geom_line()+
  geom_point()+
  geom_hline(yintercept=40)+
  annotate("text", x = "Feb", y = 40, label = "Previous Level", vjust = -0.5)

Solution

to make the horizontal line dashed and red the following arguments should be included in the geom_hline function call:

linetype = 'dotted', col = 'red'

# Sample Data 

library(tidyverse)
Month= c("Jan","Feb","Mar","Apr","May","Jun")
a = c(11,10,9,8,4,8)

test= data_frame(Month,a) 
test$cum_total <- cumsum(test$a)

test$Month <- factor(test$Month, month.abb)

# ggplot

ggplot(data=test, aes(x=Month, y=cum_total, group=1)) +
  geom_line()+
  geom_point()+
  geom_hline(yintercept=40, linetype='dotted', col = 'red')+
  annotate("text", x = "Feb", y = 40, label = "Previous Level", vjust = -0.5)

Comments

[teunbrand]

Replace your geom_hline() with geom_hline(yintercept = 40, linetype = 2, colour = "red") and it should be dashed and red.

[Rob]

Why should he do that?

[Kresten]

Updated the answer

[Rob]

I still don't see any explanation as to why he should do that

[James Hirschorn]

I would change it to linetype = 'dashed'.