S3 object system in R Programming - Mini Project: Build & Apply

Understanding the S3 Object System in R

📖 Scenario: You are working with R and want to understand how the S3 object system works. You will create a simple S3 class, add a method, and then use it to see how R decides which function to run based on the object class.

🎯 Goal: Build a simple S3 class called person with a print method that shows a custom message when printing the object.

📋 What You'll Learn

Create a list object with specific named elements

Assign a class attribute to the object

Write a print method for the S3 class

Call the print method by printing the object

💡 Why This Matters

🌍 Real World

S3 objects are used in many R packages to represent data with custom behaviors, such as data frames, time series, and model results.

💼 Career

Understanding S3 helps you extend R packages, write your own classes, and customize how data is displayed and processed in data science and statistical programming jobs.

1

Create a list object with class 'person'

Create a list called person1 with elements name set to "Alice" and age set to 30. Then assign the class person to person1 using class(person1) <- "person".

R Programming

# Create the list person1 with name and age, then assign class 'person'
# Your code here

Need a hint?

Use list() to create the object and class() to assign the class.

2

Write a print method for class 'person'

Write a function called print.person that takes one argument x and prints the message "Person: " followed by the person's name and age in parentheses. Use cat() to print the message.

R Programming

person1 <- list(name = "Alice", age = 30)
class(person1) <- "person"

# Write print.person function here
# Your code here

Need a hint?

Define print.person as a function with argument x. Use cat() to print the formatted string.

3

Call the print method by printing the object

Use the print() function to print the object person1. This should call your custom print.person method.

R Programming

person1 <- list(name = "Alice", age = 30)
class(person1) <- "person"

print.person <- function(x) {
  cat("Person: ", x$name, " (", x$age, " years old)\n", sep = "")
}

# Print person1 to see the custom message
# Your code here

Need a hint?

Simply call print(person1) to trigger the S3 print method.

4

Display the output of printing the S3 object

Run the code to display the output of printing person1. The output should be exactly Person: Alice (30 years old).

R Programming

person1 <- list(name = "Alice", age = 30)
class(person1) <- "person"

print.person <- function(x) {
  cat("Person: ", x$name, " (", x$age, " years old)\n", sep = "")
}

print(person1)
# Observe the output above

Need a hint?

Check the console output matches exactly the expected message.