SevenDailyJavaScript.js

// 1. How to check if one array has all elements of another?

var importedEmails = ['john@doe.com', 'janet@doe.com'],
  existingEmails = ['john@doe.com', 'janet@doe.com', 'fred@mercury.com'];
if(!_.difference(importedEmails, existingEmails).length) console.log('already imported')
// > already imported

// **********************************************************

// 2. How to find what elements are common to two arrays?

var tagsPost1 = ['ruby', 'rails', 'test'];
var tagsPost2 = ['test', 'rspec'];
_.intersection(tagsPost1, tagsPost2);
// > ["test"]

// **********************************************************

// 3. How to merge two Arrays without duplicating entries? 

var followeds1 = [1, 2, 3],
  followeds2 = [2, 4, 5];
_.union(followeds1, followeds2);
// > [1, 2, 3, 4, 5]

// **********************************************************

// 4. How to sort an Array of Hashes?

var data = [
  {
    name: 'Christophe',
    location: 'Belgium'
   },
   {
    name: 'John',
    location: 'United States of America'
   },
   {
    name: 'Piet',
    location: 'Belgium'
   },
   {
    name: 'François',
    location: 'France'
   }
];
_.sortBy(data, 'location');
// > [
//   { location: "Belgium", name: "Christophe" },
//   { location: "Belgium", name: "Piet" },
//   { location: "France", name: "François" },
//   { location: "United States of America", name: "John" }
// ]

// **********************************************************

// 5. How to keep objects in an Array that are unique with respect to one attribute?

var Product = function(id, categoryId){this.id = id; this.categoryId = categoryId; };
var products = [
  new Product(1, 1),
  new Product(2, 2),
  new Product(3, 3),
  new Product(4, 1),
  new Product(5, 3),
  new Product(6, 5),
];
products = _.uniq(products, 'categoryId');
// > [
//   Product {categoryId: 1, id: 1},
//   Product {categoryId: 2, id: 2},
//   Product {categoryId: 3, id: 3},
//   Product {categoryId: 5, id: 6},
// ]

// **********************************************************

//6. How to filter an Array with a string?

var books = [
 'The Ruby Programming Language',
 'Programming Ruby 1.9 & 2.0: The Pragmatic Programmers\' Guide (The Facets of Ruby)',
 'Practical Object-Oriented Design in Ruby: An Agile Primer',
 'Eloquent Ruby',
 'Ruby on Rails Tutorial: Learn Web Development with Rails'
];
_.filter(books, function(book){ return book.match(/[Rr]ails/); });
//> ["Ruby on Rails Tutorial: Learn Web Development with Rails"]

// **********************************************************

//7. How to always get an Array?

var method = function (){
  // ...
  return [].concat(products);
};