How does R handle S3 and S4 object systems?

The S3 and S4 object systems in R are two different approaches to object-oriented programming. The S3 system is simpler and more flexible, allowing for quick and easy creation of objects and methods without strict formalism. S4, on the other hand, is more formal and rigorous, requiring explicit class and method definitions, and providing better error checking and validation.

# Example of S3 object system
# Creating an S3 class
person <- list(name = "John", age = 30)
class(person) <- "Person"

# Defining a print method for the S3 class
print.Person <- function(obj) {
    cat("Name:", obj$name, "\nAge:", obj$age, "\n")
}

# Using the S3 object
print(person)

In this S3 example, a simple object person is created and assigned the class “Person”. A custom print method is then defined for objects of class “Person”. The S4 system, while more complex, allows for greater control and precision in object definitions, including slot validation and formal method definitions.