ggplot2::geom_segment. How to set multiple sizes, say c(10,12)?

Question

I'm plotting with ggplot a data frame of different actions (A,B) not mutually exclusive and have multiple Ids. The activities often overlap within an Id, which might cause that some are not visible.

The data

df <- data.frame(id = c("id1", "id1", "id2", "id2"), x1 = c(10, 9, 12, 12 ), x2 = c(16, 17, 15, 19), type = c("A", "B", "A", "B"))

The codes

library("ggplot2")

This works:

ggplot2::ggplot() +
  geom_segment(data = df, aes(colour = type, x = x1, xend = x2, y = id, yend = id), size = 10)

Result: overlapping B and A. How to specify different geom_segment size?

Does not work:

ggplot2::ggplot() +
  geom_segment(data = df, aes(colour = type, x = x1, xend = x2, y = id, yend = id), size = c(10,12,10,12))

Error: Aesthetics must be either length 1 or the same as the data (2): size

Answer 1

It looks like your sizes map to activity types. In that case you can just put size=type in the aesthetic mapping like any other part of your graph, and then specify how the different sizes will work using scale_size_discrete:

# Put all data and aesthetics that apply to the whole plot in the original
#   ggplot() call
ggplot2::ggplot(data = df, aes(colour = type, x = x1, xend = x2, y = id, yend = id, size=type)) +
    geom_segment() +
    # A is drawn first so make it bigger
    scale_size_discrete(range=c(12, 8))

Result:

Answer 2

ggplot2::ggplot() +
  geom_segment(data = df[df$type=="A", ], aes(colour = type, x = x1, xend = x2, y = id, yend = id), size = 12)+
  geom_segment(data = df[df$type=="B", ], aes(colour = type, x = x1, xend = x2, y = id, yend = id), size = 6)