Javascript ES6 (ES0215) .map(), .reduce(), .filter() usage examples.

index.js

// FILTER
/* 
If i already have an array but i only want to have items in the array that match certain criteria, use the filter.
Quando eu já tenho um array e quero apenas itens no novo array que correspondem a uma condição, use filter.
*/

// GET JUST EVEN NUMBERS

let arr = [-200, -163, -26, -4, 0, 7, 76];

let evens = arr.filter(function(x) {
   return x % 2 === 0;
});

// Arrow function
let evens = arr.filter(x => x % 2 === 0);

// Using external function
function isEven(value) {
  return value % 2 === 0;
}
let evens = arr.filter(isEven);

// MAP
/*
If i already have an array and i want to do the exact same operation on each of the elements in the array and return the same amount of items in the array, use the map.
Se eu já tenho um array e quero fazer uma mesma operação em cada elemento do array e retorna a mesma quantidade de itens do array, use map.
*/

// MULTIPLY ALL ARRAY VALUES

let arr1 = [1, 2, 3, 4];

let mult = arr1.map(function (value){
  return value * 3;
});

// Arrow function

let mult = arr1.map(value => value * 3);

// REDUCE
/*
If i already have an array, but i want to use the values in that array to create something completely new, use the reduce.
Se eu já tenho um array, mas eu quero usar os valores deste array para criar algo completamente novo, use reduce.
*/

// SUM UP THE POPULATION OF EVERY COUNTRY EXCEPT CHINA?

let data = [
  {
    country: 'China',
    pop: 1409517397,
  },
  {
    country: 'India',
    pop: 1339180127,
  },
  {
    country: 'USA',
    pop: 324459463,
  },
  {
    country: 'Indonesia',
    pop: 263991379,
  }
];

let sum = data.reduce((acc, val) => {
  return val.country == 'China' ? acc : acc + val.pop;
}, 0);

// SUM TOTAL PILOTS YEARS

let pilots = [
  {
    id: 10,
    name: "Poe Dameron",
    years: 14,
  },
  {
    id: 2,
    name: "Temmin 'Snap' Wexley",
    years: 30,
  },
  {
    id: 41,
    name: "Tallissan Lintra",
    years: 16,
  },
  {
    id: 99,
    name: "Ello Asty",
    years: 22,
  }
];

let alYears = pilots.reduce((acc, pilot) => acc + pilot.years, 0);

/*
REFERENCES
DESCRIPTIONS: https://hackernoon.com/understanding-map-filter-and-reduce-in-javascript-5df1c7eee464
FILTER EVEN NUMBERS EXAMPLE: https://stackoverflow.com/a/51876403
REDUCE POPULATION EXAMPLE: https://codeburst.io/learn-understand-javascripts-reduce-function-b2b0406efbdc
REDUCE PILOTS YEARS EXAMPLE: https://medium.com/poka-techblog/simplify-your-javascript-use-map-reduce-and-filter-bd02c593cc2d
*/