Getting Started, Part II

R and More Quarto

September 22, 2024

Plan for Today

A little more about R
Go over three examples on Posit Cloud
Discuss advanced use of Quarto
Make and publish a Quarto document on Quarto Pub

A Little More About R

What is an Object?

An object in R is a data structure used to store data
It can vary from simple scalar types to more complex data structures like vectors, lists, or data frames
Objects hold not only data but also information about the type of data and the operations that can be performed on them
Every entity in R is considered an object, making R a language based around the manipulation of objects

How to Store Data

In R, you can store data in objects using the assignment operator <-
The object name is on the left of <-, and the data or value you wish to assign to the object is on the right
Then you can print the object to the console using the object name

# Store the value 42 in the object my_number
my_number <- 42

# Print the value of my_number
my_number

[1] 42

What Can R Do?

R is a powerful language for data analysis and visualization
It is also a general-purpose programming language
It can be used for web development, machine learning, and more
It is open-source and has a large community of users and developers

R as a Calculator

R can be used as a simple calculator
You can perform arithmetic operations on numbers

# Addi a number and store it to a value
sum_of_2plus2 <- 2 + 2


sum_of_2plus2

[1] 4

When to Store Data in Objects

Note that you don’t always have to store data in objects
You should mostly store data in objects when you want to use the data later
If you only need to use the data once, you can just use the data directly

# Add two numbers without storing them in an object
2 + 2

[1] 4

Some Common Arithmetic Operators

+ addition
- subtraction
* multiplication
/ division
^ exponentiation (also **)

Functions

A function is a set of instructions that produces some output
In R, you can use built-in functions to perform specific tasks
For example, you can use the mean() function to calculate the average of a set of numbers
To do this you have to use the combine function c() to create a vector of numbers

Create a vector of numbers and take the mean…

# Create a vector of numbers
numbers <- c(1, 2, 3, 4, 5)

# Calculate the mean of the numbers
mean(numbers)

[1] 3

Some Common Base R Functions

mean() calculates the mean of a set of numbers
median() calculates the median of a set of numbers
sd() calculates the standard deviation of a set of numbers
sum() calculates the sum of a set of numbers
length() calculates the length of a vector
max() and min() calculate the maximum and minimum values of a vector
round() rounds a number to a specified number of decimal places
sqrt() calculates the square root of a number
log() calculates the natural logarithm of a number
exp() calculates the exponential of a number
abs() calculates the absolute value of a number

Your Turn!

Start a new code chunk your Quarto document
Try storing some numbers as a vector and printing the result
Try using some arithmetic operators
Try using some of the common base R functions

03:00

Three Examples

Let’s get going . . .

Let’s open up the Getting Started module on Posit Cloud…

And work through the examples there.

Example: Make a Map!

Example: Make a map!

library(leaflet)
leaflet() |> 
  addTiles() |>   # Add default OpenStreetMap map tiles
  addMarkers(lat = 38.90243843683386, lng =  -77.0443814477152, 
             label = "Elliott School of International Affairs")

03:00

Example: Plotting Democracy Over Time

# Load the packages
library(vdemlite)
library(ggplot2)

# Use vdemlite to extract democracy scores for France and INdia
dem_data <- fetchdem(indicators = "v2x_polyarchy",
                     countries = c("FRA", "IND"))

# And now we can plot the data
ggplot(dem_data, aes(y = v2x_polyarchy, x = year, color=country_name)) +
  geom_line() +
  theme_minimal() +
  xlab("Year") +
  ylab("Electoral Democracy Index") +
  ggtitle("Electoral Democracy, 1970-2022") +
  geom_hline(yintercept = .5, linetype = "dashed", color = "grey") +
   scale_color_manual(name="Country", values=c("#E69F00", "#56B4E9")) +
  ylim(0, 1)

03:00

Example: UN Voting Trends

library(tidyverse)
library(unvotes)
library(lubridate)
library(scales)
library(pacman)

unvotes <- un_votes %>%
  inner_join(un_roll_calls, by = "rcid") %>%
  inner_join(un_roll_call_issues, by = "rcid")

unvotes %>%
  # then filter out to only include the countries we want
  filter(country %in% c("South Africa", "United States", "France")) %>%
  # then make sure R understands the the year variable is a data
  mutate(year = year(date)) %>%
  # Then group the data by country and year
  group_by(country, year, issue) %>%
  # then take the average Yes votes for each country_year
  summarize(percent_yes = mean(vote == "yes")) %>%
  # then make a nice plot
  ggplot(mapping = aes(x = year, y = percent_yes, color = country)) +
  geom_point(alpha = 0.4) +
  geom_smooth(method = "loess", se = FALSE) +
  facet_wrap(~issue) +
  scale_y_continuous(labels = percent) +
  scale_color_manual( values=c("#E69F00", "#56B4E9", "#009E73")) +
  labs(
    title = "Percentage of 'Yes' votes in the UN General Assembly",
    subtitle = "1946 to 2019",
    y = "% Yes",
    x = "Year",
    color = "Country"
  )

03:00

More About Quarto

Advanced HTML

So far we have been using the basic HTML elements to create our documents
Quarto supports a wide range of HTML elements and attributes
We can use these to create more complex and interactive documents

Formatting Options

We can make our documents have a more sophisticated feel by specifying various options in the YAML header
Examples include title, subtitle, date, abstract, toc, etc.
We can also specify font styles and colors and control other aspects of the formatting
See this page to explore the various formatting options

Themes

Quarto supports a wide range of themes
We can use these to change the look and feel of our documents
Check out this page to explore the various themes available in Quarto

Footnotes

You can also add footnotes to your document
Use the ^[] or [^1] syntax to add a footnote
There are different ways to add footnotes
I find that inline notes are the easiest to work with
- For example ^[This is a footnote]

Generating Lorem Ipsum

For working on your document’s format it is helpful to have random text
The lorem package is helpful for this
You can also install an R Studio Addin

Publishing on Quarto Pub

Quarto Pub is a platform for publishing Quarto documents
You can publish your documents on Quarto Pub and share them with others
Quarto Pub is free to use
Sign up for an account, then publish with quarto publish quarto-pub name-of-document.qmd in the terminal

Your Turn!

Start a new Quarto project
Create a new Quarto document in your project folder
Add a YAML header with the following options:
- title:
- subtitle:
- date:
- date-format:
- theme:
- toc:

Your Turn!

Try adding at least one more option to your YAML header
Generate some sections and some random text using the lorem package
Add some code chunks to your document (and some code)
Add some footnotes to your document
Render the document and see what it looks like
Publish to Quarto pub