Make it Classy (1)

As well as simply retrieving the class, the class() function can be used to override it. The syntax is

class(x) <- "some_class"

This is particularly useful for lists, since lists can be used to combine other variables into more complex variables. (Remember the Lego analogy: individual variables are like Lego pieces, and you can use lists to build whatever you like.)

In this exercise, you'll look at an object to store the state of a chess game, and override its class.

To make sense of the exercise, you need to know a little bit about chess.

There are two players in a chess game, named "white" and "black".
Each player has six types of piece: a king, a queen, bishops, knights, rooks, and pawns.
The position of each piece can be recorded using the row ("a" to "h") and the column (1 to 8).

This exercise is part of the course

Object-Oriented Programming with S3 and R6 in R

View Course

Exercise instructions

The list variable chess has been predefined in your workspace.

Explore chess to understand its structure.
Override the class of chess to be "chess_game".
Check whether or not chess is still a list, using is.list() (docs).
Determine the number of pieces still left on the board.
- A good approach is to flatten the object using unlist() (docs) and return its length() (docs).

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# Explore the structure of chess
str(chess)

# Override the class of chess
___ <- ___

# Is chess still a list?
___

# How many pieces are left on the board?
___

Edit and Run Code