Graph info

Should I use this graph?


This graph requires:

✅ a categorical variable

✅ a numeric (continuous) variable

Description

If we want to plot density curves but retain the interpretability of the axes, consider comparing multiple distributions using the ggridges package.

Getting set up

PACKAGES:

Install packages.

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

DATA:

Artwork by @allison_horst

Remove missing island from penguins

Code 
peng_ridges <- filter(penguins, !is.na(island))
glimpse(peng_ridges)
Rows: 344
Columns: 8
$ species           <fct> Adelie, Adelie, Adelie, Adelie, Adelie, Adelie, Adel…
$ island            <fct> Torgersen, Torgersen, Torgersen, Torgersen, Torgerse…
$ bill_length_mm    <dbl> 39.1, 39.5, 40.3, NA, 36.7, 39.3, 38.9, 39.2, 34.1, …
$ bill_depth_mm     <dbl> 18.7, 17.4, 18.0, NA, 19.3, 20.6, 17.8, 19.6, 18.1, …
$ flipper_length_mm <int> 181, 186, 195, NA, 193, 190, 181, 195, 193, 190, 186…
$ body_mass_g       <int> 3750, 3800, 3250, NA, 3450, 3650, 3625, 4675, 3475, …
$ sex               <fct> male, female, female, NA, female, male, female, male…
$ year              <int> 2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007…

The grammar

CODE:

Create labels with labs()

Initialize the graph with ggplot() and provide data

Map bill_length_mm to the x axis

Map island to the y axis and fill

Add the ggridges::geom_density_ridges() layer (with alpha set to 2/3)

Remove the legend with show.legend = FALSE

Code 
labs_ridges <- labs(
  title = "Adult foraging penguins",
  x = "Bill length (millimeters)",
  y = "Island", fill = "Island")
ggp2_ridges <- ggplot(data = peng_ridges,
       aes(x = bill_length_mm, 
           y = island, 
        fill = island)) +
  ggridges::geom_density_ridges(alpha = 2/3, 
      show.legend = FALSE)
ggp2_ridges + 
  labs_ridges

GRAPH:

Ridgeline plots are excellent for comparing continuous distributions across groups.