38  Grouped bubble graph

This graph is largely complete and just needs final proof reading.

This graph requires:

✅ a categorical variable

✅ two numeric (continuous) variables

38.1 Description

Grouped bubble graphs use position, color, and size to display the relationships between four variables (three numerical/quantitative, one categorical).

The position on the x and y axis captures the relationship between two numerical variables. The size and color of the points display a third numerical variable across the levels of a (fourth) categorical variable.

38.2 Set up

PACKAGES:

Install packages.

install.packages("palmerpenguins")
library(palmerpenguins)
library(ggplot2)

DATA:

Artwork by allison horst

The penguins data.

penguins <- palmerpenguins::penguins
glimpse(penguins)
#> Rows: 344
#> Columns: 8
#> $ species           <fct> Adelie, Adelie, Adelie…
#> $ island            <fct> Torgersen, Torgersen, …
#> $ bill_length_mm    <dbl> 39.1, 39.5, 40.3, NA, …
#> $ bill_depth_mm     <dbl> 18.7, 17.4, 18.0, NA, …
#> $ flipper_length_mm <int> 181, 186, 195, NA, 193…
#> $ body_mass_g       <int> 3750, 3800, 3250, NA, …
#> $ sex               <fct> male, female, female, …
#> $ year              <int> 2007, 2007, 2007, 2007…

38.3 Grammar

CODE:

• Create labels with labs()

• Initialize the graph with ggplot() and provide data

• Map bill_length_mm to the x axis and flipper_length_mm to the y axis

• Inside geom_point()

  • map body_mass_g to size and species to fill

  • set the alpha to 2/3

• In the scale_size()

  • set range to c(.04, 6)

labs_grp_bubble <- labs(
  title = "Bill Length vs. Flipper Length",
  x = "Bill Length (mm)", 
  y = "Flipper length (mm)", 
  size = "Body Mass", 
  fill = "Species")

ggp2_grp_bubble <- penguins |> 
  ggplot(aes(
    x = bill_length_mm, y = flipper_length_mm)) + 
  geom_point(
    aes(size = body_mass_g, 
        color = species), 
            alpha = 2/3) + 
  scale_size(range = c(.04, 6)) 

ggp2_grp_bubble + 
  labs_grp_bubble

GRAPH:

38.4 More info

We can change the shape of the points for more control of the color and fill.

38.4.1 Shape

Inside geom_point(), we can set shape to 21, and color to "#000000" to outline the points in black

ggp2_grp_bubble_s21 <- penguins |> 
  ggplot(aes(
    x = bill_length_mm, y = flipper_length_mm)) + 
  geom_point(
    aes(size = body_mass_g, fill = species), 
        alpha = 2/3, shape = 21, color = "#000000") + 
  scale_size(range = c(.04, 6)) 

ggp2_grp_bubble_s21 + 
  labs_grp_bubble

38.4.2 Color

Inside the aes() of geom_point(), we can set shape to 21, and map color to "species" to outline the points in the same colors as fill

ggp2_grp_bubble_s21_color <- penguins |> 
  ggplot(aes(
    x = bill_length_mm, y = flipper_length_mm)) + 
  geom_point(
    aes(size = body_mass_g, 
        fill = species, 
        color = species), 
        alpha = 2/3, shape = 21) + 
  scale_size(range = c(.04, 6)) 

ggp2_grp_bubble_s21_color + 
  labs_grp_bubble