library(tidyverse)

df1 <- tibble(wt=4, mpg=25)
df2 <- tibble(wt=2, mpg=15)

ggplot(mtcars, aes(x=wt, y=mpg)) + 
    geom_point() +
    geom_point(data=df1, aes(x=wt, y=mpg), color="red", size=3) +
    geom_point(data=df2, aes(x=wt, y=mpg), color="blue", size=3)

Is there a way in ggplot that I can manually add a legend for the df1 and df2 data points as I have demo’d below (albeit using Preview)?

I can get a legend by binding the dataframes together …

df1 <- tibble(wt=4, mpg=25, source='My Car')
df2 <- tibble(wt=2, mpg=15, source='Your Car')
df <- bind_rows(mtcars, df1, df2)

ggplot(df, aes(x=wt, y=mpg, color = source)) + 
    geom_point() 

… but I often find I want to manually add a legend, but am unsure of how to do so except in an outside tool like Google Slides.