Grammar of graphics II

Jeff Stevens

2023-04-03

Introduction

Set-up

Seven components/layers of ggplots

  • Data
  • Mappings – maps data to properties of geom
  • Geom – represents data
  • Stat – transforms data
  • Position – control placement of data on coordinate
  • Facet – split graph into subplots
  • Coordinate – places data in coordinate system

Aesthetics

Map data to visual properties

Map data columns to plot

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point()

Size

Map data to aesthetic

mpg |>
  ggplot(aes(x = displ, y = hwy, size = cty)) +
  geom_point()

Apply to all points

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point(size = 0.5)

Transparency

Map data to aesthetic

mpg |>
  ggplot(aes(x = displ, y = hwy, alpha = cty)) +
  geom_point()

Apply to all points

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point(alpha = 0.25)

Shape

Map data to aesthetic

mpg |>
  ggplot(aes(x = displ, y = hwy, shape = class)) +
  geom_point()

Apply to all points

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point(shape = 5)

Shapes

Color

Map data to aesthetic

mpg |>
  ggplot(aes(x = displ, y = hwy, color = class)) +
  geom_point()

Apply to all points

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point(color = "dodgerblue")

Color

What happens if we put it in the aesthetic?

mpg |>
  ggplot(aes(x = displ, y = hwy, color = "dodgerblue")) +
  geom_point()

Color: points, lines, text, and borders

Map data to aesthetic

mpg |>
  ggplot(aes(x = class, color = class)) +
  geom_bar(show.legend = FALSE, linewidth = 2)

Apply to everything

mpg |>
  ggplot(aes(x = class)) +
  geom_bar(color = "blue", linewidth = 2)

Fill: filled areas

Map data to aesthetic

mpg |>
  ggplot(aes(x = class, fill = class)) +
  geom_bar(show.legend = FALSE)

Apply to everything

mpg |>
  ggplot(aes(x = class)) +
  geom_bar(fill = "blue")

Lines

Separated by groups

mpg |>
  ggplot(aes(x = displ, y = hwy, group = drv)) +
  geom_smooth()

Linetype

mpg |>
  ggplot(aes(x = displ, y = hwy, linetype = drv)) +
  geom_smooth()

Apply line aesthetics to groups

mpg |>
  ggplot(aes(x = displ, y = hwy, color = drv)) +
  geom_smooth(show.legend = FALSE)

Apply aesthetics to one geom

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point(aes(color = class)) +
  geom_smooth()

Apply aesthetics differently to geoms

mpg |>
  ggplot(aes(x = displ, y = hwy, color = drv)) +
  geom_point() +
  geom_smooth(aes(linetype = drv))

Bands have aesthetics, too

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point() +
  geom_smooth(aes(color = drv, fill = drv))

Statistical transformations

Statistical transformations

  • ggplot can calculate statistics on the fly
  • many geoms have underlying statistical transformation
diamonds
# A tibble: 53,940 × 10
   carat cut       color clarity depth table price     x     y     z
   <dbl> <ord>     <ord> <ord>   <dbl> <dbl> <int> <dbl> <dbl> <dbl>
 1  0.23 Ideal     E     SI2      61.5    55   326  3.95  3.98  2.43
 2  0.21 Premium   E     SI1      59.8    61   326  3.89  3.84  2.31
 3  0.23 Good      E     VS1      56.9    65   327  4.05  4.07  2.31
 4  0.29 Premium   I     VS2      62.4    58   334  4.2   4.23  2.63
 5  0.31 Good      J     SI2      63.3    58   335  4.34  4.35  2.75
 6  0.24 Very Good J     VVS2     62.8    57   336  3.94  3.96  2.48
 7  0.24 Very Good I     VVS1     62.3    57   336  3.95  3.98  2.47
 8  0.26 Very Good H     SI1      61.9    55   337  4.07  4.11  2.53
 9  0.22 Fair      E     VS2      65.1    61   337  3.87  3.78  2.49
10  0.23 Very Good H     VS1      59.4    61   338  4     4.05  2.39
# ℹ 53,930 more rows

Bar plots

Count observations of variable types with stat_count()

diamonds |>
  ggplot(aes(x = cut)) +
  geom_bar()

Summarize data

stat_summary()

diamonds |>
  ggplot(aes(x = cut, y = depth)) +
  geom_point()

Plot mean and standard error

diamonds |>
  ggplot(aes(x = cut, y = depth)) +
  stat_summary()

Summarize data

Plot mean and 95% CI

diamonds |>
  ggplot(aes(x = cut, y = depth)) +
  stat_summary(fun.data = mean_cl_normal)

Plot median and range

diamonds |>
  ggplot(aes(x = cut, y = depth)) +
  stat_summary(fun.min = min, fun.max = max, fun = median)

Facets

Facets

Coloring by group difficult to visualize with many groups

mpg |>
  ggplot(aes(x = displ, y = hwy, color = class)) +
  geom_point()

Facet

Pulls out groups into separate panels

mpg |>
  ggplot(aes(x = displ, y = hwy)) +
  geom_point() +
  facet_wrap(~ class)

Let’s code!

Grammar of graphics II [Rmd]

DPaViR 2023