ggplot2: How to create dashed lines in legend?

Question

I am trying to create a ggplot consisting of 2 densities with straight lines and 2 dashed densities. 2 densities are blue and the other 2 are red. My plot should include a legend with colors and lines in respect to these densities.

Even though I think there must be an easy solution, I am not able to produce dashed lines in my legend. I tried to solve my issue based on several threads, eg here or here , but my ggplot code is already kind of complex and the examples of these threads use ggplot in different ways. Hence, I didn't manage to reproduce the results of these threads.

Here is a reproducible example of what I did so far. The last line with scale_linetype_manual seems not to work. How could I produce dashed lines in my legend for grp3 and grp4?

library(ggplot2)

set.seed(123)

# Example data
N <- 1000
x1 <- rnorm(N, 5)
x2 <- rnorm(N, 10)
x3 <- rnorm(N, 15)
x4 <- rnorm(N, 20)

ggplot() + 
  stat_density(aes(x = x1, col = "grp1"), position = "identity", geom = "line") + 
  stat_density(aes(x = x2, col = "grp2"), position = "identity", geom = "line") +
  stat_density(aes(x = x3, col = "grp3"), position = "identity", geom = "line", linetype = 2) +
  stat_density(aes(x = x4, col = "grp4"), position = "identity", geom = "line", linetype = 2) +
  theme_bw() +
  theme(axis.text.y = element_text(angle = 90, hjust = 0.3), 
        axis.title.x = element_text(vjust = - 0.5), 
        plot.title = element_text(vjust = 1.5), 
        legend.title = element_blank(), legend.position = c(0.75, 0.85), 
        legend.key = element_blank(), legend.text = element_text(size = 10)) + 
  scale_color_manual(values = c("red", "dodgerblue3", "red", "dodgerblue3")) + 
  scale_linetype_manual(values = c("grp1" = 1, "grp2" = 1, "grp3" = 2, "grp4" = 2))

Answer 1

library(reshape)
library(ggplot2)
N <- 1000
x1 <- rnorm(N, 5);  x2 <- rnorm(N, 10);  x3 <- rnorm(N, 15);  x4 <- rnorm(N, 20)

df1 <- data.frame(x1,x2,x3,x4)
df2 <- melt(df1)

ggplot(data=df2,aes(x=value, col=variable, linetype=variable)) +
 stat_density(position = "identity", geom = "line") +
  theme_bw() +
  theme(axis.text.y = element_text(angle = 90, hjust = 0.3), 
        axis.title.x = element_text(vjust = - 0.5), 
        plot.title = element_text(vjust = 1.5), 
        legend.title = element_blank(), 
        legend.key = element_blank(), legend.text = element_text(size = 10)) +
  scale_color_manual(values = c("red", "dodgerblue3", "red", "dodgerblue3")) + 
  scale_linetype_manual(values = c(1, 1, 2, 2)) +
  theme(legend.key.size =  unit(0.5, "in"))

Answer 2

If you convert it to a dataframe with a grouping column, you can do this using the method in this answer .

Here is the code:

library(ggplot2)
library(dplyr)

set.seed(123)

# Example data
N <- 1000
x1 <- rnorm(N, 5)
x2 <- rnorm(N, 10)
x3 <- rnorm(N, 15)
x4 <- rnorm(N, 20)

df <- data.frame(x = c(x1, x2, x3, x4), 
                 group = rep(c("grp1", "grp2", "grp3", "grp4"), each = N))

df %>%
  ggplot(aes(x, color = group)) +
  geom_density(aes(linetype = group)) +
  scale_color_manual(name = "Treatment & State",
                      labels = c("grp1", "grp2", "grp3", "grp4"),
                      values = c("red", "dodgerblue3", "red", "dodgerblue3")) +   
  scale_linetype_manual(name = "Treatment & State",
                     labels = c("grp1", "grp2", "grp3", "grp4"),
                     values = c("grp1" = 1, "grp2" = 1, "grp3" = 2, "grp4" = 2))

That gives you this image