ggplot2 - adding lines of same color but different type to legend

Question

Given some data like:

my.data <- data.frame(time     = rep(1:3, 2),
                      means    = 2:7,
                      lowerCI  = 1:6,
                      upperCI  = 3:8,
                      scenario = rep(c("A","Z"), each=3))
my.data
#     time means lowerCI upperCI scenario
# 1    1     2       1       3        A
# 2    2     3       2       4        A
# 3    3     4       3       5        A
# 4    1     5       4       6        Z
# 5    2     6       5       7        Z
# 6    3     7       6       8        Z

I need to make a plot like the one below but some label for the (confidence) dotted lines should appear in the legend - the order matters, should be something like Z, A, CI-Z, CI-A (see below). This is the corresponding code:

ggplot(data = my.data) +
# add the average lines
geom_line(aes(x=time, y=means, color=scenario)) +
# add "confidence" lines
geom_line(aes(x=time, y=lowerCI, color=scenario), linetype="dotted") +
geom_line(aes(x=time, y=upperCI, color=scenario), linetype="dotted") +
# set color manually
scale_color_manual(name = 'Scenario',
                   breaks = c("Z", "A"),
                   values = c("Z"  = "red",
                              "A"  = "blue"))

Below is my attempt after I checked this & this SO similar questions. I get close enough, but I want the "CI" labels not to be separate.

ggplot(data = my.data) +
# add the average lines
geom_line(aes(x=time, y=means, color=scenario)) +
# add "confidence" lines
geom_line(aes(x=time, y=lowerCI, color=scenario, linetype="CI")) +
geom_line(aes(x=time, y=upperCI, color=scenario, linetype="CI")) +
# set color manually
scale_color_manual(name = 'Scenario',
                   breaks = c("Z", "A"),
                   values = c("Z"  = "red",
                              "A"  = "blue")) +
# set line type manually
scale_linetype_manual(name = 'Scenario',
                      breaks = c("Z", "A", "CI"),
                      values = c("Z"  = "solid",
                                 "A"  = "solid",
                                 "CI" = "dotted"))

I also tried something using geom_ribbon, but I could not find a clear way to make it display only the edge lines and add them as desired in the legend. All in all, I don't need to display bands, but lines. I'm sure there is an obvious way, but for now I'm stuck here...

Answer 1

We can use guide_legend to specify dashed linetypes for the CI's. I think this is close to what you want:

ggplot(my.data, aes(x = time, y = means))+
    geom_line(aes(colour = scenario))+
    geom_line(aes(y = lowerCI, colour = paste(scenario, 'CI')),
              linetype = 'dashed')+
    geom_line(aes(y = upperCI, colour = paste(scenario, 'CI')),
              linetype = 'dashed')+
    scale_colour_manual(values = c('A' = 'red','Z' = 'blue',
                                   'A CI' = 'red','Z CI' = 'blue'),
                        breaks = c('Z', 'Z CI', 'A', 'A CI'))+
    guides(colour = guide_legend(override.aes = list(linetype = c('solid', 'dashed'))))+
    ggtitle('Dashed lines represent X% CI')