Day 5: What Is a Set?

Learning Goals

• Define the characteristics of a set
• Implement a common methods of a set class

Introduction

A set is a data structure that can store any number of unique values or elements. That means there are no repeating elements in a set.

Many languages provide sets as part of the core language, but today, we'll be building our own MySet class by using a hash/object as the underlying data structure. We've chosen a hash/object because that data structure only allows unique keys.

// Convert an Array to a Set

array = [1, 3, 1, 2]
set = new Set from array
=> {1, 3, 2}

Implement the MySet class

We have already declared a class called MySet in the starter files and provided the underlying data structure: a hash/object called data. You'll need to build out all of the methods. Do not worry about the ordering of items in the set. They can be in any order.

Be aware that these methods may go by different names in different languages. This is one way to implement a set, there are others! We are basing ours on JavaScript's Set class.

Initialization, e.g. constructor(iterable) or #initialize(iterable)

We should be able to initialize a new MySet instance with no data, or by providing an iterable, such as an array or string. When a new MySet instance is initialized with an array or string, only its unique contents should be added to the MySet instance.

Use a value of true for each key: { dog: true }.

new MySet()
=> MySet data = {}
new MySet([1, 2, 1, 3])
=> MySet data = { 1: true, 2: true, 3: true }
new MySet('hello')
=> MySet data = { 'h': true, 'e': true, 'l': true, 'o': true }

An error should be thrown if a user tries to initialize a new MySet instance with anything other than nothing, a string, or an array.

size

Returns the number of items in the MySet instance.

add(item)

Add an item to a MySet instance. Remember, only unique items should exist in MySet. When adding an item, the item is added as is. Return the MySet instance.

my_set = new MySet()
my_set.add('caat')
=> MySet data = { 'caat' }

next_set = new MySet('doooog')
next_set.add('caarp')
=> MySet data = { 'd', 'o', 'g', 'caarp' }
next_set.add(12)
=> MySet data = { 'd', 'o', 'g', 'caarp', 12 }

Note on JS: Arrays cannot be keys for JS objects. They will be converted to strings by default like so: [1, 2] => '1,2'. Don't worry about this. We'll ensure our tests allow for this. For now, just be aware that actual Sets most certainly can handle Arrays!

delete(item)

Removes the item from the set. If the removal was successful, return true. If the item was not removed (i.e. if the item was not present in the set to begin with), return false.

my_set = new MySet('aabb')
my_set.delete('a')
=> true
my_set.delete('z')
=> false

Note on JS: Don't worry about handling Arrays here!

has(item)

If the item is in the MySet instance, return true, otherwise false.

Note on JS: Don't worry about handling Arrays here!

entries

Returns an array containing all of the values in the MySet instance.

my_set = new MySet('aabb')
my_set.entries()
=> ['a', 'b']

Note on JS: Don't worry about handling Arrays (which were meant to be keys in this.data) here!

Use the language of your choosing. We've included starter files for some languages where you can pseudocode, explain your solution and code.

And remember, don't run our tests until you've passed your own!

How to run your own tests

Ruby

1. cd into the ruby folder
2. ruby <filename>.rb

JavaScript

1. cd into the javascript folder
2. node <filename>.js

How to run our tests

Ruby

1. cd into the ruby folder
2. bundle install
3. rspec

JavaScript

1. cd into the javascript folder
2. npm i
3. npm test