Adding a second legend for vertical lines in ggplot [closed] - r

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I'm trying to add a second legend for 6 vertical lines I've added onto a ggplot2 line plot representing 1 of 2 events instead of labelling the lines using the annotate function. I've tried this code but I'm not having much look:
p<- data %>%
ggplot(aes(variable, value)) +
geom_line(aes(color = size, group = size)) +
geom_vline(xintercept = c(1,9,11), linetype="dashed") +
geom_vline(xintercept = c(5,14,17), linetype="dotted") +
scale_linetype_manual(name = 'Events',
values = c('Closures' = 3,
'Opening' = 3))

Answer 1

A good way to do this could be to use mapping= to create the second legend in the same plot for you. The key is to use a different aesthetic for the vertical lines vs. your other lines and points.
First, the example data and plot:
library(ggplot2)
library(dplyr)
library(tidyr)
set.seed(8675309)
df <- data.frame(x=rep(1:25, 4), y=rnorm(100, 10, 2), lineColor=rep(paste0("col",1:4), 25))
base_plot <-
df %>%
ggplot(aes(x=x, y=y)) +
geom_line(aes(color=lineColor)) +
scale_color_brewer(palette="Greens")
base_plot
Now to add the vertical lines as OP has done in their question:
base_plot +
geom_vline(xintercept = c(1,9,11), linetype="dotted",
color = "red", size=1) +
geom_vline(xintercept = c(5,14,17), linetype="dotted",
color = "blue", size=1)
To add the legend, we will need to add another aesthetic in mapping=. When you use aes(), ggplot2 expects that mapping to contain the same number of observations as the dataset specified in data=. In this case, df has 100 observations, but we only need 6 lines. The simplest way around this would be to create a separate small dataset that's used for the vertical lines. This dataframe only needs to contain two columns: one for xintercept and the other that can be mapped to the linetype:
verticals <- data.frame(
intercepts=c(1,9,11,5,14,17),
Events=rep(c("Closure", "Opening"), each=3)
)
You can then use that in code with one geom_vline() call added to our base plot:
second_plot <- base_plot +
geom_vline(
data=verticals,
mapping=aes(xintercept=intercepts, linetype=Events),
size=0.8, color='blue',
key_glyph="path" # this makes the legend key horizontal lines, not vertical
)
second_plot
While this answer does not use color to differentiate the vertical lines, it's the most in line with the Grammar of Graphics principles which ggplot2 is built upon. Color is already used to indicate the differences in your data otherwise, so you would want to separate out the vertical lines using a different aesthetic. I used some of these GG principles putting together this answer - sorry, the color palette is crap though lol. In this case, I used a sequential color scale for the lines of data, and a different color to separate out the vertical lines. I'm showing the vertical line size differently than the lines from df to differentiate more and use the linetype as the discriminatory aesthetic among the vertical lines.
You can use this general idea and apply the aesthetics as you see best for your own data.

Answer 2

What about geom_label?
library(tidyverse)
data <- tribble(
~x, ~label,
1, "first",
1.5, "second",
5, "third"
)
data %>%
ggplot(aes(x = x, y = 1)) +
geom_vline(aes(xintercept = x)) +
geom_label(aes(label = label))
Created on 2021-12-13 by the reprex package (v2.0.1)