Grouped box plots
Description
Grouped box plots display five different statistical measures across a series of categories, or groups, of a discrete, ordinal, or interval variable.
The five statistical measures are 1) the first quartile, 2) the second quartile, and 3) the third quartile. The fourth and fifth values are the largest/smallest values no further than 1.5 X inter-quartile range from the hinges.
Getting set up
PACKAGES:
Install packages.
Code
install.packages("palmerpenguins")
library(palmerpenguins)
library(ggplot2)
DATA:
Remove the missing island
values from the penguins
data.
Code
<- filter(penguins, !is.na(island))
peng_box glimpse(peng_box)
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 island
to the x
axis and to fill
Map bill_length_mm
to the y
axis
Add geom_boxplot()
and set the alpha
to 2/3
Remove the legend with show.legend = FALSE
Code
<- labs(
labs_grp_boxplots title = "Adult foraging penguins",
subtitle = "Palmer Archipelago, Antarctica",
x = "Island", fill = "Island",
y = "Bill length (millimeters)")
<- ggplot(data = peng_box,
ggp2_grp_boxplots aes(x = island,
y = bill_length_mm,
fill = island)) +
geom_boxplot(alpha = 2/3,
show.legend = FALSE)
+
ggp2_grp_boxplots labs_grp_boxplots
GRAPH:
When a categorical variable is supplied, the plot will contain a box for each level or group.
More info
NOTCHES:
Add notches to the box plot using the notch = TRUE
and notchwidth
arguments.
Code
<- ggplot(data = peng_box,
ggp2_grp_box_notch aes(x = island,
y = bill_length_mm,
fill = island)) +
geom_boxplot(
notch = TRUE,
notchwidth = 0.85,
alpha = 2/3,
show.legend = FALSE)
+
ggp2_grp_box_notch labs_grp_boxplots
OUTLIERS:
Box plots display outliers using points, and we can change the color these using the outlier.colour
argument. Inside the geom_boxplot()
, we map island
to color
and set outlier.colour
to NULL
:
Code
<- ggplot(data = peng_box,
ggp2_grp_box_outliers aes(x = island,
y = bill_length_mm,
fill = island)) +
geom_boxplot(aes(color = island),
outlier.colour = NULL,
outlier.size = 2,
notch = TRUE,
notchwidth = 0.85,
alpha = 2/3,
show.legend = FALSE)
+
ggp2_grp_box_outliers labs_grp_boxplots