Most useful Array methods

forEach.js

var arr = ['javascript','css','html'];

function printSkill(element, index) {
	console.log(element + ' is the ' + index + ' element in the array');
}

arr.forEach(printSkill);

keys.js

var obj = { 'skill': 'javascript',
            'user': 'Bill'
          };

console.log(Object.keys(obj)); // ["skill", "user"]

map.js

var arr = ['10', '20', '30'];

function returnCube(ele) {
     return ele * ele * ele;
}

var intArr = arr.map(returnCube); // [1000, 8000, 27000]

push.js

var arr = ['Bill', 'Chad'];
arr.push('Sue'); // 4
console.log(arr); // ["Bill", "Chad", "Sue"]

reduce.js

function returnSum(previousValue, currentValue) {
  return previousValue + currentValue;
}

var sum = [0, 1, 2, 3, 4].reduce(returnSum); 

console.log(sum); // 10

shift.js

var arr = ['Bill', 'Chad', 'Sue'];
var shiftedArr = arr.shift(); // "Bill"
console.log(arr); // ["Chad", "Sue"]

transform.js

// Given an endorsment array with objects containing skill and user keys 
var endorsements = [
  { skill: 'javascript', user: 'Chad' },
  { skill: 'javascript', user: 'Bill' },
  { skill: 'javascript', user: 'Sue' },
  { skill: 'html', user: 'Sue HTML' },
  { skill: 'css', user: 'Sue CSS' },
  { skill: 'css', user: 'Bill CSS' }
];
 
// And we want to transform an given endorsment array with an array which is a collection of objects with key skill and users
// But user key is an array containing all the users with that particular skill
[
  { skill: 'javascript', user: [ 'Chad', 'Bill', 'Sue' ], count: 3 },
  { skill: 'css', user: [ 'Sue', 'Bill' ], count: 2 },
  { skill: 'html', user: [ 'Sue' ], count: 1 } 
]; 

// Array methods: forEach(), map(), push()
// Object methods: Object.keys()

function transformData (endo) {
    
    var tra = {};
    
    endo.forEach(function(el) {
        if (tra[el.skill]) {
          tra[el.skill].push(el.user);
        } else {
          tra[el.skill] = [];
          tra[el.skill].push(el.user);
        }
    });	

    var res = Object.keys(tra).map(function(key) {    	
        var obj = {};
        obj['skills'] = key;
        obj['values'] = tra[key];
      	return obj;
    });
    
    console.log(res);
}

transformData(endorsements);