图例未出现在 ggplot2 中

Question

I have the following code:

ggplot(TC_merge, aes(x=Location)) + 
  geom_line(aes(y = C_r_base), color = "black", linetype="dashed") + 
  geom_line(aes(y = C_a_base), color = "navyblue") +
  geom_line(aes(y = C_a_after), color = "red4") + theme_classic() + 
  theme(legend.position="right") +
  labs(x = "Distance from CBD (kilometres)",
       y = "Round-trip generalised transport costs (DKK)") + 
  scale_x_continuous(expand = c(0, 0)) +
  scale_y_continuous(expand = c(0, 0)) +
  theme(text=element_text(family="Cambria", size=12)) 

And I get the following graph (without legend):

Picture

Here is the data:

Location C_r_base C_a_base C_a_after
0.01     59.09    80.0629  57.5824
0.02     54.18    80.1257  57.6648
0.03     54.27    80.1886  57.7473
0.04     54.36    80.2515  57.8297

I know the data has to be tidy for the legend to work, but rail still has to be a dotted line in the legend, so I'm not sure how to make that distinction manually.

Answer 1

All you needed to do is move the color param inside the aes

library(ggplot2)

# Sample data using dput
TC_merge <- structure(list(Location = c(0.01, 0.02, 0.03, 0.04), C_r_base = c(59.09, 
  54.18, 54.27, 54.36), C_a_base = c(80.0629, 80.1257, 80.1886, 
    80.2515), C_a_after = c(57.5824, 57.6648, 57.7473, 57.8297)), row.names = c(NA, 
      -4L), class = "data.frame")

# create the manual color scale
manual_color_scale <- c("black", "navyblue", "red4")
names(manual_color_scale) <- c("black", "navyblue", "red4")

ggplot(TC_merge, aes(x=Location)) + 
  # Here I move the color param inside - Though it is a value.
  # The actual color could be random generated.
  # So it is needed to define the color scale
  geom_line(aes(y = C_r_base, color = "black"),  linetype="dashed",
            # I use the size for bigger line to see the color better
            size = 1) + 
  geom_line(aes(y = C_a_base, color = "navyblue"), size = 1) +
  geom_line(aes(y = C_a_after, color = "red4"), size = 1) + theme_classic() + 
  theme(legend.position="right") +
  labs(x = "Distance from CBD (kilometres)",
    y = "Round-trip generalised transport costs (DKK)") + 
  scale_x_continuous(expand = c(0, 0)) +
  scale_y_continuous(expand = c(0, 0)) +
  # Here I defined the manual scale for color
  scale_color_manual(values = manual_color_scale) +
  theme(text=element_text(family="Cambria", size=12))

Here is the plot with legend

^{Created on 2021-03-31 by the reprex package (v1.0.0)}