为什么 scale_linetype_manual() 会巧妙地改变线型美学？

Question

I want to manually specify the linetypes for a fixed ordering of factors (so changing the underlying factor ordering is not an option).

library(ggplot2)

df = data.frame(x = rep(1:10, 3),
                y = c(runif(10), runif(10), runif(10)), 
                z = c(rep("a", 10), rep("b", 10), rep("c", 10)))

ggplot(df, aes(x, y, linetype = z)) + geom_line()

ggplot(df, aes(x, y, linetype = z)) + 
           geom_line() +      
           scale_linetype_manual(values = c("solid", "dotted", "dashed"))

These are not the same.

1. Why not?

2. How do I make them the same?

R version 4.1.2 (2021-11-01)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.4

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

other attached packages:
[1] ggplot2_3.3.5 

Answer 1

The simple answer is that the three linetypes you have chosen are not the default line types. The linetype palette is generated by scales::linetype_palette . The first 3 values are:

scales::linetype_pal()(3)
#> [1] "solid" "22"    "42"

So you can replicate the default by doing:

ggplot(df, aes(x, y, linetype = z)) + 
  geom_line() +
  theme_minimal() +
  scale_linetype_manual(values = scales::linetype_pal()(3))

^{Created on 2022-06-22 by the reprex package (v2.0.1)}