scale_linetype_manual: Merging legends is difficult

[ptoche]

I'm finding it difficult to merge a scale_linetype_manual with the other guides.

1. I'm incompetent or tired or both
2. The docs could have one or two examples of usage for scale_linetype_manual (I don't see any at this time)

library("ggplot2")

df <- structure(list(year = c(1990, 2000, 2010, 2020, 2030, 2040), 
                     variable = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = "Something", class = "factor"), 
                     value = c(4, 5, 6, 7, 8, 9), category = structure(c(1L, 1L, 
                                                                         1L, 2L, 2L, 2L), .Label = c("Observed", "Projected"), class = "factor"), 
                     category2 = structure(c(NA, NA, 1L, 1L, NA, NA), .Label = "Transition", class = "factor")), row.names = c(NA, 
                                                                                                                               6L), class = "data.frame")

df.sub <- na.omit(df)

# First attempt:
ggplot(data = df, aes(x = year, y = value)) + 
    geom_point(aes(group = category, colour = category, shape = category), size = 4) +
    geom_line(aes(group = category, colour = category), size = 1) +
    geom_line(data = df.sub, aes(linetype = ""), 
              group = 1, colour = "black", size = 1) +
    scale_linetype_manual(name = "category", values = "dotted", labels = "Transition")

# Second attempt:
ggplot(data = df, aes(x = year, y = value)) + 
    geom_point(aes(group = category, colour = category, shape = category), size = 4) +
    geom_line(aes(group = category, colour = category, linetype = ""), size = 1) + 
    geom_line(data = df.sub, aes(linetype = category2), 
              group = 1, colour = "black", size = 1) + 
    scale_linetype_manual(name = "category", values = c("solid", "dashed", "solid"), labels = c("Observed", "Transition", "Projected"))

^{Created on 2021-05-07 by the reprex package (v2.0.0)}

[iagogv3]

Maybe related to SO questions https://stackoverflow.com/questions/50293125/r-change-ggplot-legend-names-with-scale-linetype-manual, https://stackoverflow.com/questions/68540054/how-to-modify-the-linetype-of-the-legend-of-hline-in-ggplot2 and issue #4479 ?

[thomasp85]

You are right that merging manual legends are pretty difficult. The key is to make sure that all scales have the exact same title and breaks....

Down the line it would be nice to have a more flexible guide system but this is a pretty big effort unrelated to this particular issue