# map function

city_lengths = map(len, ['sanjose', 'cupertino', 'sunnyvale', 'fremont'])

print(list(city_lengths))

​

# [7, 9, 9, 7]

# Map takes a function and a collection of items. It makes a new, empty collection, runs the function on each item in the original collection and inserts each return value into the new collection. It returns the new collection.

The map() method creates a new array populated with the results of calling 

a provided function on every element in the calling array.

​

const array1 = [1, 4, 9, 16];

​

// pass a function to map

const map1 = array1.map(x => x * 2);

​

console.log(map1);

// expected output: Array [2, 8, 18, 32]

const array = [2, 5, 9];

let squares = array.map((num) => num * num);

​

console.log(array); // [2, 5, 9]

console.log(squares); // [4, 25, 81]

/* Answer to: "javascript map function" */

​

/*

  <Array>.map() - One of the most useful in-built methods in JavaScript (imo).

​

  The map() method creates a new array populated with the results of calling

  a provided function on every element in the calling array.

  For more information, click on the source link.

​

  Let me make some examples of it's uses:

*/

​

let array = [1, 4, 9, 16];

array.map(num => num * 2); // [2, 8, 18, 32];

array.map(pounds => `£${pounds}.00`); // ["£1.00", "£4.00", "£9.00", "£16.00"];

array.map(item => Math.sqrt(item)); // [1, 2, 3, 4];

function map(array, transform) {

  let mapped = [];

  for (let element of array) {

    mapped.push(transform(element));

  }

  return mapped;

}

​

let rtlScripts = SCRIPTS.filter(s => s.direction == "rtl");

console.log(map(rtlScripts, s => s.name));

// → ["Adlam", "Arabic", "Imperial Aramaic", …]

var number = [1, 2 , 3, 4, 5, 6, 7, 8, 9]; 

var doubles  = number.map((n) => { return n*2 })

​

/*  doubles 

    (9) [2, 4, 6, 8, 10, 12, 14, 16, 18] */

const myMap = new Map();

let userid = 1314124141;

​

myMap.set('veri_' + userid, 1) // set

myMap.set('veri_' + userid, myMap.get('veri_' + userid) + 1) // push

​

console.log(myMap.get('veri_' + userid)) // output: 3

const myAwesomeArray = [5, 4, 3, 2, 1]

​

myAwesomeArray.map(x => x * x)

​

// >>>>>>>>>>>>>>>>> Output: [25, 16, 9, 4, 1]

// Create a Map

const fruits = new Map([

  ["apples", 500],

  ["bananas", 300],

  ["oranges", 200]

]);

var rebels = pilots.filter(function (pilot) {  return pilot.faction === "Rebels";});var empire = pilots.filter(function (pilot) {  return pilot.faction === "Empire";});