R rotate vline in ggplot legend with scale_linetype_manual

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I have the following simple MWE. I want the green line in my legend to be a vertical line. Once I enable show.legend in geom_vline, it also adds a vertical line to every other line in the legend. Does anyone have a hint on how I can achieve this?

library(ggplot2)
ggplot(data = df) +
  geom_line(aes(x = a, y = b, colour = "one", linetype = "one"), size = 2) +
  geom_line(aes(x = a, y = c, colour = "two", linetype = "two"), size = 2) +
  geom_vline(aes(xintercept = 0.5, colour = "three", linetype = "three"), alpha = 1, show.legend = F) +
  scale_colour_manual("",
                      breaks = c("one", "two", "three"),
                      values = c("blue", "red", "green")) +
  scale_linetype_manual("",
                        breaks = c("one", "two", "three"),
                        values = c("dashed", "solid", "solid")) +
  theme_bw() +
  theme(legend.key.size = unit(2, "cm"),
        legend.position = c(0.05, 0.995), legend.justification = c(0.05, 0.995))

enter image description here

ggplot2 r
1 Answers

Adapting this answer one option to achieve your desired result would be to make use of a custom key glyph function. One drawback of this approach is that it conditions on the color of the line to choose between a horizontal or vertical line, i.e. that means that if you change the colors you have to adjust the condition too.

EDIT To get right line sizes in the legend there are two options. One would be to set the sizes in the custom key glyph function. A second option would be to set the size via the override.aes argument of guide_legend using guides(linetype = guide_legend(override.aes = list(size = c(2, 2, .5))))

library(ggplot2)

# Custom Key Glyph. Vertical Line if color = "green". Horizontal Line otherwise
draw_key_cust <- function(data, params, size) {
  if (data$colour == "green") {
    data$size <- .5
    draw_key_vpath(data, params, size)
  } else {
    data$size <- 2
    draw_key_path(data, params, size)
  }
}

ggplot(data = df) +
  geom_line(aes(x = a, y = b, colour = "one", linetype = "one"), size = 2, key_glyph = "cust") +
  geom_line(aes(x = a, y = c, colour = "two", linetype = "two"), size = 2, key_glyph = "cust") +
  geom_vline(aes(xintercept = 0.5, colour = "three", linetype = "three"), alpha = 1, key_glyph = "cust") +
  scale_colour_manual(breaks = c("one", "two", "three"),
                      values = c("blue", "red", "green")) +
  scale_linetype_manual(breaks = c("one", "two", "three"),
                        values = c("dashed", "solid", "solid")) +
  labs(color = NULL, linetype = NULL) +
  theme_bw() +
  theme(legend.key.size = unit(2, "cm"),
        legend.position = c(0.05, 0.995), 
        legend.justification = c(0.05, 0.995))

DATA

set.seed(42)
df <- data.frame(
  a = runif(100),
  b = runif(100),
  c = runif(100)
)
user_129938610
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