In ggplot2, remove superfluous points from line legend

Question

I have this plot:

library(ggplot2)
ggplot(iris,
       aes(
           x = Petal.Length,
           y = Petal.Width,
           color = Species,
           linetype = Species,
           shape = Species
       )) +
    geom_count(alpha = 0.20) +
    geom_smooth(method = "lm", se = FALSE) + 
    labs(
        color = "Species (Line)",
        linetype = "Species (Line)",
        shape = "Species (Points)"
    )  +
    guides(
        size = "none"
        )
#> `geom_smooth()` using formula = 'y ~ x'

^{Created on 2023-11-02 with reprex v2.0.2}

I am trying to format the legend so that there is a legend that has point shapes (by color also) and a separate legend for linetype (also by color).

What I actually get is a legend just for shapes (with no color) and a legend for linetype that has colored points. I have tried every iteration of legend labelling that I can think of, to no avail.

Question: Keeping everything else the same, how could I get rid of those points in the Species (Line) legend? And how to add color to the shapes?

Answer 1

You'll need to remove the color guide and override the aesthetics of the shape and linetype guide:

library(ggplot2)

ggplot(iris,
       aes(
         x = Petal.Length,
         y = Petal.Width,
         color = Species,
         linetype = Species,
         shape = Species
       )) +
  geom_count(alpha = 0.20) +
  geom_smooth(method = "lm", se = FALSE) + 
  labs(
    linetype = "Species (Line)",
    shape = "Species (Points)"
  )  +
  guides(
    size = "none",
    color = "none",
    shape = guide_legend(override.aes = list(alpha = 1, 
                                             color =  scales::hue_pal()(3))),
    linetype = guide_legend(override.aes = list(color =  scales::hue_pal()(3)))
  )

However, I might humbly suggest that the reason you have this difficulty is that you are mapping the same variable onto multiple aesthetics. This is completely unnecessary for a clear and legible plot - flipping backwards and forwards between two legends to interpret a plot just makes it harder on the reader, not easier. I would recommend getting rid of the chartjunk, perhaps something like:

library(geomtextpath)

ggplot(iris, aes(x = Petal.Length, y = Petal.Width, group = Species)) +
  geom_count(alpha = 0.3, aes(color = Species)) +
  geom_textsmooth(aes(label = Species), method = "lm", se = FALSE, 
                  vjust = -0.2, size = 6) +
  scale_size_area() +
  guides(size = "none", color = "none") +
  theme_classic(base_size = 20)

I think this demonstrates the data more clearly.