Problem: qqplot legend different linetypes - r

Question

legend <- c("score" = "black", "answer" = "red")
plot <- df_l %>% ggplot(aes(date, score, color = "score")) + geom_line() +
geom_vline(aes(xintercept = getDate(df_all %>% filter(name == List[5])), color = "answer"), linetype = "dashed", size = 1,) +
scale_color_manual(name = "Legend", values = legend) +
scale_x_date(labels = date_format("%m/%y"), breaks = date_breaks("months")) +
theme(axis.text.x = element_text(angle=45)) +
labs(title = "", x = "", y = "", colors = "Legend")
I get the result above and could not figure out how to resolve the problem that in the legend always both lines are mixed up. One legend should of course show the slim black line only and the other the dashed black line. Thanks in advance!

Answer 1

The issue you have is that geom_vline results in a legend item that is a vertical line and geom_line gives you a horizontal line item. One solution is to create the legend kind of manually by specifying the color= aesthetic in geom_line... but not in geom_vline. You can then create a kind of "dummy" geom with geom_blank that serves as a holding object for the aesthetics of color=. You can then specify the colors for both of those items via scale_color_manual. Here's an example:
set.seed(12345)
df <- data.frame(x=1:100,y=rnorm(100))
ggplot(df, aes(x,y)) + theme_bw() +
geom_line(aes(color='score')) +
geom_vline(aes(xintercept=4), linetype=2, color='red', show.legend = FALSE) +
geom_blank(aes(color='my line')) +
scale_color_manual(name='Legend', values=c('my line'='red','score'='black'))
That creates the one legend for color... but unfortunately "my line" is solid red, when it should be dashed. To fix that, you just apply the linetype= aesthetic in the same way.
ggplot(df, aes(x,y)) + theme_bw() +
geom_line(aes(color='score', linetype='score')) +
geom_vline(aes(xintercept=4), linetype=2, color='red', show.legend = FALSE) +
geom_blank(aes(color='my line', linetype='my line')) +
scale_linetype_manual(name='Legend', values=c('my line'=2,'score'=1)) +
scale_color_manual(name='Legend', values=c('my line'='red','score'='black'))