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