Create additional independent legends in ggplot2 - r

Question

I have been struggling with this for hours now. I have the following script:
library(ggplot2)
sims = replicate(1000, sample(c(0,0,0,0,1,1,1,2,2,2), size=3, replace=FALSE))
df = data.frame(x=colSums(sims == 0),
y=colSums(sims == 1))
df$count <- 1
total_counts = aggregate(count ~ ., df, FUN = sum)
min_count = min(total_counts$count)
max_count = max(total_counts$count)
p = (ggplot(df, aes(x=x, y=y))
+ geom_count(aes(color=..n.., size=..n..), alpha=0.8)
+ guides(color = 'legend', size=FALSE)
+ labs(color='Count')
+ scale_colour_gradient(limits = c(min_count, max_count),
breaks = round(seq(min_count, max_count, length.out=5)),
labels = round(seq(min_count, max_count, length.out=5)))
+ scale_size_continuous(range = c(3, 7.5))
)
So far so good. The problem is that I want to add two additional sets of points:
df2 = data.frame(x=c(0, 1, 2, 3),
y=c(1.5253165, 1.0291262, 0.4529617, 0))
df3 = data.frame(x=c(0, 1, 2, 3),
y=c(1.5, 1, 0.5, 0))
To get something like this:
p2 = (p
+ geom_point(data=df2, aes(x=x, y=y), alpha=0.4, color="red", size = 2.5)
+ geom_point(data=df3, aes(x=x, y=y), alpha=0.4, color="green", size = 2.5)
)
The problem is that I am not being capable of adding these new points to the legend. I would like the legend to be in a different "section". Namely, to have an empty string title (to differentiate these points from "Count" title), and to have strings instead of numbers in their labels ("Simulated means" and "Theoretical means", for example).
Is there any way to achieve this?

Answer 1

A trick I learned from #tjebo is that you can use the ggnewscale package to spawn additional legends. At what point in plot construction you call the new scale is important, so you first want to make a geom/stat layer and add the desired scale. Once these are declared, you can use new_scale_colour() and all subsequent geom/stat layers will use a new colour scale.
library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 4.0.5
library(ggnewscale)
#> Warning: package 'ggnewscale' was built under R version 4.0.3
sims = replicate(1000, sample(c(0,0,0,0,1,1,1,2,2,2), size=3, replace=FALSE))
df = data.frame(x=colSums(sims == 0),
y=colSums(sims == 1))
df$count <- 1
total_counts = aggregate(count ~ ., df, FUN = sum)
min_count = min(total_counts$count)
max_count = max(total_counts$count)
df2 = data.frame(x=c(0, 1, 2, 3),
y=c(1.5253165, 1.0291262, 0.4529617, 0))
df3 = data.frame(x=c(0, 1, 2, 3),
y=c(1.5, 1, 0.5, 0))
ggplot(df, aes(x, y)) +
geom_count(aes(colour = after_stat(n), size = after_stat(n)),
alpha = 0.5) +
scale_colour_gradient(
limits = c(min_count, max_count),
breaks = round(seq(min_count, max_count, length.out = 5)),
labels = round(seq(min_count, max_count, length.out = 5)),
guide = "legend"
) +
new_scale_colour() +
geom_point(aes(colour = "Simulated means"),
data = df2, alpha = 0.4) +
geom_point(aes(colour = "Theoretical means"),
data = df3, alpha = 0.4) +
scale_colour_discrete(
name = ""
) +
scale_size_continuous(range = c(3, 7.5), guide = "none")
Created on 2021-04-22 by the reprex package (v1.0.0)
(P.S. sorry for reformatting your code, it just read more easily for myself this way)