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<div align="center">
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<h1> 30 Days Of JavaScript</h1>
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<a class="header-badge" target="_blank" href="https://www.linkedin.com/in/asabeneh/">
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<img src="https://img.shields.io/badge/style--5eba00.svg?label=LinkedIn&logo=linkedin&style=social">
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</a>
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<a class="header-badge" target="_blank" href="https://twitter.com/Asabeneh">
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<img alt="Twitter Follow" src="https://img.shields.io/twitter/follow/asabeneh?style=social">
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</a>
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<sub>Author:
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<a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
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<small> January, 2020</small>
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</sub>
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</div>
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[<< Day 9](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/09_Day/09_day_higher_order_functions.md) | [Day 11>>](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/11_Day/11_day_destructuring_and_spread.md)
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- [Day 10](#day-10)
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- [Set](#set)
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- [Creating an empty set](#creating-an-empty-set)
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- [Creating set from array](#creating-set-from-array)
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- [Adding an element to a set](#adding-an-element-to-a-set)
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- [Deleting an element a set](#deleting-an-element-a-set)
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- [Checking an element in the set](#checking-an-element-in-the-set)
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- [Clearing the set](#clearing-the-set)
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- [Union of sets](#union-of-sets)
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- [Intersection of sets](#intersection-of-sets)
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- [Difference of sets](#difference-of-sets)
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- [Map](#map)
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- [Creating an empty Map](#creating-an-empty-map)
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- [Creating an Map from array](#creating-an-map-from-array)
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- [Adding values to the Map](#adding-values-to-the-map)
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- [Getting a value from Map](#getting-a-value-from-map)
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- [Checking key in Map](#checking-key-in-map)
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- [Exercises](#exercises)
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- [Exercises:Level 1](#exerciseslevel-1)
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- [Exercises:Level 2](#exerciseslevel-2)
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- [Exercises:Level 3](#exerciseslevel-3)
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# Day 10
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## Set
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Set is a collection a collection of elements. Set can only contains unique elements.
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Lets see how to create a set
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### Creating an empty set
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```js
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const companies = new Set()
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console.log(companies)
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```
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```sh
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{}
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```
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### Creating set from array
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```js
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const languages = [
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'English',
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'Finnish',
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'English',
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'French',
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'Spanish',
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'English',
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'French'
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]
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const setOfLangauges = new Set(languages)
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console.log(setOfLangauges)
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```
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```sh
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Set(4) {"English", "Finnish", "French", "Spanish"}
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```
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Set is an iterable object and we can iterate through each elements.
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```js
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const languages = [
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'English',
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'Finnish',
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'English',
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'French',
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'Spanish',
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'English',
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'French'
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]
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const setOfLangauges = new Set(languages)
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for (const language of setOfLangauges) {
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console.log(language)
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}
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```
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```sh
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English
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Finnish
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French
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Spanish
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```
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### Adding an element to a set
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```js
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const companies = new Set() // creating an empty set
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console.log(companies.size) // 0
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companies.add('Google') // add element to the set
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companies.add('Facebook')
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companies.add('Amazon')
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companies.add('Oracle')
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companies.add('Microsoft')
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console.log(companies.size) // 5 elements in the set
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console.log(companies)
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```
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```sh
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Set(5) {"Google", "Facebook", "Amazon", "Oracle", "Microsoft"}
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```
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We can also use loop to add element to a set.
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```js
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const companies = ['Google', 'Facebook', 'Amazon', 'Oracle', 'Microsoft']
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setOfCompanies = new Set()
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for (const company of companies) {
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setOfCompanies.add(company)
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}
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```
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```sh
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Set(5) {"Google", "Facebook", "Amazon", "Oracle", "Microsoft"}
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```
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### Deleting an element a set
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We can delete an element from a set using a delete method.
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```js
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console.log(companies.delete('Google'))
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console.log(companies.size) // 4 elements left in the set
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```
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### Checking an element in the set
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The has method can help to know if a certain element exists in a set.
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```js
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console.log(companies.has('Apple')) // false
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console.log(companies.has('Facebook')) // true
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```
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### Clearing the set
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It removes all the elements from a set.
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```js
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companies.clear()
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console.log(companies)
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```
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```sh
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{}
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```
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See the example below to learn how to use set.
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```js
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const languages = [
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'English',
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'Finnish',
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'English',
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'French',
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'Spanish',
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'English',
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'French'
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]
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const langSet = new Set(languages)
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console.log(langSet) // Set(4) {"English", "Finnish", "French", "Spanish"}
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console.log(langSet.size) // 4
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const counts = []
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const count = {}
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for (const l of langSet) {
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const filteredLang = languages.filter(lng => lng === l)
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console.log(filteredLang) // ["English", "English", "English"]
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counts.push({ lang: l, count: filteredLang.length })
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}
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console.log(counts)
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```
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```js
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[
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{ lang: 'English', count: 3 },
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{ lang: 'Finnish', count: 1 },
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{ lang: 'French', count: 2 },
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{ lang: 'Spanish', count: 1 }
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]
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```
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Other use case of set. For instance to count unique item in an array.
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```js
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const numbers = [5, 3, 2, 5, 5, 9, 4, 5]
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const setOfNumbers = new Set(numbers)
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console.log(setOfNumbers)
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```
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```sh
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Set(5) {5, 3, 2, 9, 4}
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```
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### Union of sets
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To find a union to two sets can be achieved using spread operator. Lets find the union of set A and set B (A U B)
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```js
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let a = [1, 2, 3, 4, 5]
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let b = [3, 4, 5, 6]
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let c = [...a, ...b]
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let A = new Set(a)
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let B = new Set(b)
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let C = new Set(c)
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console.log(C)
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```
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```sh
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Set(6) {1, 2, 3, 4, 5,6}
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```
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### Intersection of sets
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To find an intersection of two sets can be achieved using filter. Lets find the union of set A and set B (A ∩ B)
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```js
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let a = [1, 2, 3, 4, 5]
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let b = [3, 4, 5, 6]
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let A = new Set(a)
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let B = new Set(b)
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let c = a.filter(num => B.has(num))
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let C = new Set(c)
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console.log(C)
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```
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```sh
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Set(3) {3, 4, 5}
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```
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### Difference of sets
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To find an the difference between two sets can be achieved using filter. Lets find the different of set A and set B (A \ B)
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```js
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let a = [1, 2, 3, 4, 5]
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let b = [3, 4, 5, 6]
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let A = new Set(a)
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let B = new Set(b)
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let c = a.filter(num => !B.has(num))
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let C = new Set(c)
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console.log(C)
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```
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```sh
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Set(2) {1, 2}
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```
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## Map
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### Creating an empty Map
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```js
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const map = new Map()
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console.log(map)
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```
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```sh
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Map(0) {}
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```
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### Creating an Map from array
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```js
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countries = [
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['Finland', 'Helsinki'],
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['Sweden', 'Stockholm'],
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['Norway', 'Oslo']
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]
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const map = new Map(countries)
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console.log(map)
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console.log(map.size)
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```
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```sh
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Map(3) {"Finland" => "Helsinki", "Sweden" => "Stockholm", "Norway" => "Oslo"}
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3
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```
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### Adding values to the Map
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```js
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const countriesMap = new Map()
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console.log(countriesMap.size) // 0
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countriesMap.set('Finland', 'Helsinki')
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countriesMap.set('Sweden', 'Stockholm')
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countriesMap.set('Norway', 'Oslo')
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console.log(countriesMap)
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console.log(countriesMap.size)
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```
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```sh
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Map(3) {"Finland" => "Helsinki", "Sweden" => "Stockholm", "Norway" => "Oslo"}
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3
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```
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### Getting a value from Map
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```js
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console.log(countriesMap.get('Finland'))
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```
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```sh
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Helsinki
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```
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### Checking key in Map
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Check if a key exist in a map using *has* method. It returns *true* or *false*.
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```js
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console.log(countriesMap.has('Finland'))
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```
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```sh
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true
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```
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Getting all values from map using loop
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```js
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for (const country of countriesMap) {
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console.log(country)
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}
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```
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```sh
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(2) ["Finland", "Helsinki"]
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(2) ["Sweden", "Stockholm"]
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(2) ["Norway", "Oslo"]
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```
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```sh
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for (const [country, city] of countriesMap){
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console.log(country, city)
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}
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```
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```sh
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Finland Helsinki
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Sweden Stockholm
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Norway Oslo
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```
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🌕 You established a big milestone, you are unstoppable. Keep going! You have just completed day 10 challenges and you are 10 steps a head in to your way to greatness. Now do some exercises for your brain and for your muscle.
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## Exercises
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### Exercises:Level 1
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```js
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const a = {4, 5, 8, 9}
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const b = {3, 4, 5, 7}
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const countries = ['Finland', 'Sweden', 'Norway']
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```
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1. create an empty set
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2. Create a set containing 0 to 10 using loop
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3. Remove an element from a set
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4. Clear a set
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5. Create a set of 5 string elements from array
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6. Create a map of countries and number of characters of a country
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### Exercises:Level 2
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1. Find a union b
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2. Find a intersection b
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3. Find a with b
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### Exercises:Level 3
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1. How many languages are there in the countries object file.
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1. \*\*\* Use the countries data to find the 10 most spoken languages:
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````js
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// Your output should look like this
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console.log(mostSpokenLanguages(countries, 10))
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[
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{'English':91},
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{'French':45},
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{'Arabic':25},
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{'Spanish':24},
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{'Russian':9},
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{'Portuguese':9},
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{'Dutch':8},
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{'German':7},
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{'Chinese':5},
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{'Swahili':4},
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{'Serbian':4}]
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// Your output should look like this
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console.log(mostSpokenLanguages(countries, 3))
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[
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{'English':91},
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{'French':45},
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{'Arabic':25}
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]
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````
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🎉 CONGRATULATIONS ! 🎉
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[<< Day 9](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/09_Day/09_day_higher_order_functions.md) | [Day 11>>](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/11_Day/11_day_destructuring_and_spread.md)
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