Module 3-1-Principle - Data Visualization with ggplot2 in R

Author

Austin Voth

Published

February 18, 2026

0.1 Loading Packages

#install.packages("ggplot2") 
#install.packages('ggrepel')
#install.packages('ggthemes') 
#install.packages('scales') 
#install.packages('lattice')
#install.packages('GGally') 
#install.packages("dplyr") 
#install.packages("tidyverse") 
#install.packages('ggtext')
#install.packages("glue") 
library(ggplot2) #visualization
library(ggrepel) #labels for data
library(ggthemes) #collections of themes
library(scales) # scale
library(plotly) # interactive chart
library(GGally) # correlation
library(dplyr) # data transformation
library(tidyverse) # mega package containing 8 packages
library(ggtext) # for text visualization
library(glue) # combining multiple component
library(gapminder)

Understand mtcars data 1.1 Using Help

?mtcars
help(mtcars)
data()

A data frame with 32 observations on 11 (numeric) variables.

[, 1]	mpg	Miles/(US) gallon
[, 2]	cyl	Number of cylinders
[, 3]	disp	Displacement (cu.in.)
[, 4]	hp	Gross horsepower
[, 5]	drat	Rear axle ratio
[, 6]	wt	Weight (1000 lbs)
[, 7]	qsec	1/4 mile time
[, 8]	vs	Engine (0 = V-shaped, 1 = straight)
[, 9]	am	Transmission (0 = automatic, 1 = manual)
[,10]	gear	Number of forward gears
[,11]	carb	Number of carburetors

1 2 Reading data and converting to a tibble (cars)

mtcar

Error:
! object 'mtcar' not found

head (mtcars) class (mtcars) # short cut for pipe operator (%>%, |>): ct] + shift + M mtcars %>% rownames_to_column () %>% as_tibbl() %>% rename (model = rowname %>% print (n = 20, width = Inf)

1.3 Simple Descriptive Statistics ::: callout-note shortcut for code chunk: ctl + alt + i :::

summary(cars)

     speed           dist       
 Min.   : 4.0   Min.   :  2.00  
 1st Qu.:12.0   1st Qu.: 26.00  
 Median :15.0   Median : 36.00  
 Mean   :15.4   Mean   : 42.98  
 3rd Qu.:19.0   3rd Qu.: 56.00  
 Max.   :25.0   Max.   :120.00

glimpse(cars)

Rows: 50
Columns: 2
$ speed <dbl> 4, 4, 7, 7, 8, 9, 10, 10, 10, 11, 11, 12, 12, 12, 12, 13, 13, 13…
$ dist  <dbl> 2, 10, 4, 22, 16, 10, 18, 26, 34, 17, 28, 14, 20, 24, 28, 26, 34…

skimr::skim(cars)

Data summary
Name	cars
Number of rows	50
Number of columns	2
_______________________
Column type frequency:
numeric	2
________________________
Group variables	None

Variable type: numeric

skim_variable	n_missing	complete_rate	mean	sd	p0	p25	p50	p75	p100	hist
speed	0	1	15.40	5.29	4	12	15	19	25	▂▅▇▇▃
dist	0	1	42.98	25.77	2	26	36	56	120	▅▇▅▂▁

Basic Plotting Methods in Base R

# Using a built in plotting function
hist(cars$disp, breaks = 10)

Error in `hist.default()`:
! 'x' must be numeric

2 Lattice package

install.packages("lattice")

Error in `contrib.url()`:
! trying to use CRAN without setting a mirror

library(lattice)
xyplot(mpt ~ wt, cars)

Error:
! object 'mpt' not found

histogram(cars$disp)

Error in `UseMethod()`:
! no applicable method for 'histogram' applied to an object of class "NULL"

2.1 ggplot2

We will use ggplot2 – the best tool in the market for data visualization – from now on.

3 4.1 Elaborate Examples

3.1 4.1.1 x & y are both continuous with moderator & labeller()

cars |> 
  count(cyl)

Error in `count()`:
! Must group by variables found in `.data`.
✖ Column `cyl` is not found.

3.1.0.1 Wrangling

easy_labels <- c("4" = "4 Cylinder Cars",
                 "6" = "6 Cylinder Cars",
                 "8" = "8 Cylinder Cars"
                 )

cars %>% 
  mutate(cyl = factor(cyl)) %>% 
  ggplot(aes(x = mpg, y = disp, color = cyl)) +
  geom_point(size=3, 
             color='black'
             ) + #geom
 # geom_jitter() +
  geom_smooth(method = lm, se = FALSE) +
 # facet_grid(cols = vars(cyl), 
  facet_wrap(~ cyl, 
             #scales = "free_y", 
             ncol = 1,
             strip.position = "top",
             labeller = labeller(cyl = easy_labels)
             ) + #faceting
  scale_y_continuous(limits = c(0, NA), expand= c(0,0)) +
  coord_flip() + #coordinate
  theme_economist() +  #labels
  labs(title = 'MPG vs Displacement', 
       x = 'Miles Per Gallon', 
       y = 'Displacement') +
  theme(
       strip.placement = "outside", 
       strip.background = element_blank(),
       panel.background = element_blank(),
       panel.grid = element_blank(),
       axis.line = element_line()
        ) +
  guides(color = 'none')

Error in `mutate()`:
ℹ In argument: `cyl = factor(cyl)`.
Caused by error:
! object 'cyl' not found

3.1.1 Plotting

cars |>
  mutate (cyl = factor(cyl)) |>
  ggplot(aes(x+ mpg, y = disp, color + cyL)) +
  geom_plot() +
  geom_smooth(method = "lm", se = FALSE) +
  facet_wrap(~ cyl, ncol = 1)

Error in `mutate()`:
ℹ In argument: `cyl = factor(cyl)`.
Caused by error:
! object 'cyl' not found

  theme_bw()

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