scale_fill versus scale_color for geom_point

I want to generate bubble plots where the bubbles have a black outline. However, for some reason, I'm having trouble getting geom_point to accept scale_fill. This gives me a nice plot where the bubble color scales with a continuous variable, color:

age <-c(16, 5, 6, 22, 11, 12, 11, 13, 4, 8)
y <- c(0.53, 0.50, 0.50, 0.46, 0.44, 0.44, 0.44, 0.43, 0.40, 0.40) 
s <- c(11.5, 78.0, 753.5, 44.5, 372.0, 62.0, 163.0, 25.0, 56.0, 80.5)
color <- c(29, 15, 7, 30, 15, 26, 8, 14, 17, 12) 

df <- data.frame(age, y, s, color)  

p <- ggplot(df)+
   geom_point(aes(x = age, y = y, size = s, color = color))+
   labs(x = "age", y = "rate")+
   scale_size(range = c(.1, 10), name="s")+
   scale_color_viridis(limits = c(5, 20), oob = squish, option = "magma")+
   scale_x_continuous(breaks=c(0, 10, 20, 30, 40, 50), limits = c(0,55))+
   scale_y_continuous(breaks=c(-0.4, -0.2, 0, 0.2, 0.4), limits=c(-0.5, 0.5))+
   theme_minimal()

But if I just switch color to fill, I get all black bubbles:

   p <- ggplot(df)+
      geom_point(aes(x = age, y = y, size = s, fill = color))+
      labs(x = "age", y = "rate")+
      scale_size(range = c(.1, 10), name="s")+
      scale_fill_viridis(limits = c(5, 20), oob = squish, option = "magma")+
      scale_x_continuous(breaks=c(0, 10, 20, 30, 40, 50), limits = c(0,55))+
      scale_y_continuous(breaks=c(-0.4, -0.2, 0, 0.2, 0.4), limits=c(-0.5, 0.5))+
      theme_minimal()

If I specify shape:

p <- ggplot(df)+
      geom_point(aes(x = age, y = y, size = s, shape = 21, fill = color))+
      labs(x = "age", y = "rate")+
      scale_size(range = c(.1, 10), name="s")+
      scale_fill_viridis(limits = c(5, 20), oob = squish, option = "magma")+
      scale_x_continuous(breaks=c(0, 10, 20, 30, 40, 50), limits = c(0,55))+
      scale_y_continuous(breaks=c(-0.4, -0.2, 0, 0.2, 0.4), limits=c(-0.5, 0.5))+
      theme_minimal()

I get

Error in scale_f(): ! A continuous variable can not be mapped to shape

If I understand correctly, fill should specify bubble color and color should let me specify a black outline around the bubbles. What am I missing here? Thanks.

Solution

Your error says that you can't assign a continuous variable to shape. You should place shape outside your aes like this:

age <-c(16, 5, 6, 22, 11, 12, 11, 13, 4, 8)
y <- c(0.53, 0.50, 0.50, 0.46, 0.44, 0.44, 0.44, 0.43, 0.40, 0.40) 
s <- c(11.5, 78.0, 753.5, 44.5, 372.0, 62.0, 163.0, 25.0, 56.0, 80.5)
color <- c(29, 15, 7, 30, 15, 26, 8, 14, 17, 12) 

df <- data.frame(age, y, s, color)  

library(ggplot2)
library(viridis)
library(scales)
p <- ggplot(df)+
  geom_point(aes(x = age, y = y, size = s, fill = color), shape = 21)+
  labs(x = "age", y = "rate")+
  scale_size(range = c(.1, 10), name="s")+
  scale_fill_viridis(limits = c(5, 20), oob = squish, option = "magma")+
  scale_x_continuous(breaks=c(0, 10, 20, 30, 40, 50), limits = c(0,55))+
  scale_y_continuous(breaks=c(-0.4, -0.2, 0, 0.2, 0.4), limits=c(-0.5, 0.5))+
  theme_minimal()
p
#> Warning: Removed 1 rows containing missing values (geom_point).

^{Created on 2022-08-29 with reprex v2.0.2}