# Nia11's solution

## to Custom Set in the Lua Track

Published at Dec 05 2018 · 0 comments
Instructions
Test suite
Solution

Create a custom set type.

Sometimes it is necessary to define a custom data structure of some type, like a set. In this exercise you will define your own set. How it works internally doesn't matter, as long as it behaves like a set of unique elements.

## Running the tests

To run the tests, run the command `busted` from within the exercise directory.

## Further information

For more detailed information about the Lua track, including how to get help if you're having trouble, please visit the exercism.io Lua language page.

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### custom-set_spec.lua

``````local Set = require('custom-set')

describe('custom-set', function()
describe('is_empty', function()
it('should indicate that an empty set is empty', function()
assert.is_true(Set():is_empty())
end)

it('should indicate that sets with elemnts are non-empty', function()
assert.is_false(Set(1):is_empty())
end)
end)

describe('contains', function()
it('should indicate that nothing is an element of an empty set', function()
assert.is_false(Set():contains(1))
end)

it('should indicate that an element is contained in a set that contains the element', function()
assert.is_true(Set(1, 2, 3):contains(1))
assert.is_true(Set(1, 2, 3):contains(2))
assert.is_true(Set(1, 2, 3):contains(3))
end)

it('should indicate that an element that is not in a set is not contained in the set', function()
assert.is_false(Set(1, 2, 3):contains(4))
end)
end)

describe('is_subset', function()
it('should indicate that an empty set is a subset of another empty set', function()
assert.is_true(Set():is_subset(Set()))
end)

it('should indicate that an empty set is a subset of a non-empty set', function()
assert.is_true(Set():is_subset(Set(1)))
end)

it('should indicate that a non-empty set is not a subset of an empty set', function()
assert.is_false(Set(1):is_subset(Set()))
end)

it('should indicate that a non-empty set is a subset of itself', function()
assert.is_true(Set(1, 2, 3):is_subset(Set(1, 2, 3)))
end)

it('should indicate that a proper subset is a subset', function()
assert.is_true(Set(1, 2, 3):is_subset(Set(4, 1, 2, 3)))
end)

it('should indicate that a set is not a subset of another set with different elements but the same element count', function()
assert.is_false(Set(1, 2, 3):is_subset(Set(4, 1, 3)))
end)
end)

describe('is_disjoint', function()
it('should indicate that the empty set is disjoint with itself', function()
assert.is_true(Set():is_disjoint(Set()))
end)

it('should indicate that the empty set is disjoint with a non-empty set', function()
assert.is_true(Set():is_disjoint(Set(1)))
end)

it('should indicate that a non-empty set is not disjoint with an empty set', function()
assert.is_true(Set(1):is_disjoint(Set()))
end)

it('should indicate that sets with an element in common are not disjoint', function()
assert.is_false(Set(1, 2):is_disjoint(Set(2, 3)))
end)

it('should indicate that sets with no elements in common are disjoint', function()
assert.is_true(Set(1, 2):is_disjoint(Set(3, 4)))
end)
end)

describe('equality', function()
it('should consider empty sets equal', function()
assert.is_true(Set():equals(Set()))
end)

it('should not consider an empty set to be equal to a non-empty set', function()
assert.is_false(Set():equals(Set(1, 2, 3)))
end)

it('should not consider a non-empty set to be equal to an empty set', function()
assert.is_false(Set(1, 2, 3):equals(Set()))
end)

it('should ignore order', function()
assert.is_true(Set(1, 3):equals(Set(3, 1)))
end)

it('should consider different sets to be different', function()
assert.is_false(Set(1, 2, 3):equals(Set(1, 2, 4)))
end)
end)

it('should allow an element to be added to an empty set', function()
local s = Set()
assert.is_true(s:contains(3))
end)

it('should allow an element to be added to a non-empty set', function()
local s = Set(1, 2, 4)
assert.is_true(s:equals(Set(1, 2, 3, 4)))
end)

it('should allow an element to be re-added to a set', function()
local s = Set(1, 2, 3)
assert.is_true(s:equals(Set(1, 2, 3)))
end)
end)

describe('intersection', function()
it('should give the empty set as the intersection of two empty sets', function()
assert.is_true(Set():intersection(Set()):equals(Set()))
end)

it('should intersect an empty set with a non-empty set', function()
assert.is_true(Set():intersection(Set(3, 2, 5)):equals(Set()))
end)

it('should intersect a non-empty set with an empty set', function()
assert.is_true(Set(1, 2, 3, 4):intersection(Set()):equals(Set()))
end)

it('should intersect a single element set with itself', function()
assert.is_true(Set(3):intersection(Set(3)):equals(Set(3)))
end)

it('should intersect sets with a single element in common', function()
assert.is_true(Set(1, 2, 3):intersection(Set(3, 4, 5)):equals(Set(3)))
end)

it('should intersect sets with a multiple elements in common', function()
assert.is_true(Set(1, 2, 3, 4):intersection(Set(3, 2, 5)):equals(Set(2, 3)))
end)

it('should intersect a set with a subset', function()
assert.is_true(Set(1, 2, 3):intersection(Set(2, 3)):equals(Set(2, 3)))
end)

it('should intersect sets with no elements in common', function()
assert.is_true(Set(1, 2, 3):intersection(Set(4, 5, 6)):equals(Set()))
end)
end)

describe('intersection', function()
it('should give the empty set as the intersection of two empty sets', function()
assert.is_true(Set():intersection(Set()):equals(Set()))
end)

it('should intersect an empty set with a non-empty set', function()
assert.is_true(Set():intersection(Set(3, 2, 5)):equals(Set()))
end)

it('should intersect a non-empty set with an empty set', function()
assert.is_true(Set(1, 2, 3, 4):intersection(Set()):equals(Set()))
end)

it('should intersect a single element set with itself', function()
assert.is_true(Set(3):intersection(Set(3)):equals(Set(3)))
end)

it('should intersect sets with a single element in common', function()
assert.is_true(Set(1, 2, 3):intersection(Set(3, 4, 5)):equals(Set(3)))
end)

it('should intersect sets with a multiple elements in common', function()
assert.is_true(Set(1, 2, 3, 4):intersection(Set(3, 2, 5)):equals(Set(2, 3)))
end)

it('should intersect a set with a subset', function()
assert.is_true(Set(1, 2, 3):intersection(Set(2, 3)):equals(Set(2, 3)))
end)

it('should intersect sets with no elements in common', function()
assert.is_true(Set(1, 2, 3):intersection(Set(4, 5, 6)):equals(Set()))
end)
end)

describe('difference', function()
it('should give the difference of two empty sets as the empty set', function()
assert.is_true(Set():difference(Set()):equals(Set()))
end)

it('should give the difference of an empty set and a non-empty set as the empty set', function()
assert.is_true(Set():difference(Set(3, 2, 5)):equals(Set()))
end)

it('should give the difference of a non-empty set and the empty set as the non-empty set', function()
assert.is_true(Set(1, 2, 3, 4):difference(Set()):equals(Set(1, 2, 3, 4)))
end)

it('should give the difference of two sets with an intersection', function()
assert.is_true(Set(3, 2, 1):difference(Set(2, 4)):equals(Set(1, 3)))
end)
end)

describe('union', function()
it('should produce the empty set as the union of two empty sets', function()
assert.is_true(Set():union(Set()):equals(Set()))
end)

it('should give the union of an empty set with another set as the other set', function()
assert.is_true(Set():union(Set(2)):equals(Set(2)))
end)

it('should give the union of a non-empty set and an empty set as the non-empty set', function()
assert.is_true(Set(1, 3):union(Set()):equals(Set(1, 3)))
end)

it('should produce the union of different sets', function()
assert.is_true(Set(1, 3):union(Set(2, 3)):equals(Set(1, 2, 3)))
end)
end)
end)``````
``````set={}
set.__index = set

function set:is_empty()
for k in pairs(self.contents) do
return false
end
return true
end

function set:contains(element)
return (self.contents[element]~=nil)
end

function set:is_subset(super)
for k in pairs(self.contents) do
if not super:contains(k) then return false end
end
return true
end

function set:is_disjoint(other)
for k in pairs(self.contents) do
if other:contains(k) then return false end
end
for k in pairs(other.contents) do
if self:contains(k) then return false end
end
return true
end

function set:equals(other)
for k in pairs(self.contents) do
if not other:contains(k) then return false end
end
for k in pairs(other.contents) do
if not self:contains(k) then return false end
end
return true
end

self.contents[element]=true
end

function set:intersection(other)
local common = {contents={}}
for k in pairs(self.contents) do
if other:contains(k) then
common.contents[k]=true
end
end
return setmetatable(common,set)
end

function set:difference(other)
for k in pairs(self.contents) do
if other:contains(k) then
self.contents[k]=nil
end
end
return setmetatable(self,set)
end

function set:union(other)
for k in pairs(other.contents) do
self.contents[k]=true
end
return setmetatable(self,set)
end

return function(...)
local args={...}
local o = {contents={}}
for k,v in pairs(args) do
o.contents[v]=true
end
return setmetatable(o,set)
end``````

### What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?
• Are there new concepts here that you could read more about to improve your understanding?