[JavaScript Array Methods: sort, map, reduce, some, every] Map calls the callback function 1 time for each element in the array. #JavaScript

jsArrayMethods.js

const inventors = [
      { first: 'Albert', last: 'Einstein', year: 1879, passed: 1955 },
      { first: 'Isaac', last: 'Newton', year: 1643, passed: 1727 },
      { first: 'Galileo', last: 'Galilei', year: 1564, passed: 1642 },
      { first: 'Marie', last: 'Curie', year: 1867, passed: 1934 },
      { first: 'Johannes', last: 'Kepler', year: 1571, passed: 1630 },
      { first: 'Nicolaus', last: 'Copernicus', year: 1473, passed: 1543 },
      { first: 'Max', last: 'Planck', year: 1858, passed: 1947 },
      { first: 'Katherine', last: 'Blodgett', year: 1898, passed: 1979 },
      { first: 'Ada', last: 'Lovelace', year: 1815, passed: 1852 },
      { first: 'Sarah E.', last: 'Goode', year: 1855, passed: 1905 },
      { first: 'Lise', last: 'Meitner', year: 1878, passed: 1968 },
      { first: 'Hanna', last: 'Hammarström', year: 1829, passed: 1909 }
    ];

const people = ['Beck, Glenn', 'Becker, Carl', 'Beckett, Samuel', 'Beddoes, Mick', 'Beecher, Henry', 'Beethoven, Ludwig', 'Begin, Menachem', 'Belloc, Hilaire', 'Bellow, Saul', 'Benchley, Robert', 'Benenson, Peter', 'Ben-Gurion, David', 'Benjamin, Walter', 'Benn, Tony', 'Bennington, Chester', 'Benson, Leana', 'Bent, Silas', 'Bentsen, Lloyd', 'Berger, Ric', 'Bergman, Ingmar', 'Berio, Luciano', 'Berle, Milton', 'Berlin, Irving', 'Berne, Eric', 'Bernhard, Sandra', 'Berra, Yogi', 'Berry, Halle', 'Berry, Wendell', 'Bethea, Erin', 'Bevan, Aneurin', 'Bevel, Ken', 'Biden, Joseph', 'Bierce, Ambrose', 'Biko, Steve', 'Billings, Josh', 'Biondo, Frank', 'Birrell, Augustine', 'Black, Elk', 'Blair, Robert', 'Blair, Tony', 'Blake, William'];

// Array.prototype.filter()
// 1. Filter the list of inventors for those who were born in the 1500's
// const fifteen = inventors.filter(inventor => inventor.year >= 1500 && inventor.year < 1600); also works
const fifteen = inventors.filter(function(inventor) {
  if (inventor.year >= 1500 && inventor.year < 1600) {
    return true;
  }
});

console.table(fifteen);

// Array.prototype.map(), map() returns a new array of the same length
// 2. Give us an array of the inventors' first and last names
const fullNames = inventors.map(inventor => {
  return inventor.first + ' ' + inventor.last;
  // or `${inventor.first} ${inventor.last}`;
})
console.table(fullNames);

// Array.prototype.sort()
// 3. Sort the inventors by birthdate, oldest to youngest
const ordered = inventors.sort(function(a, b) {
  if (a.year > b.year) { return 1; }
  else { return -1; }
  // Or use ternary operator
  // return a.year > b.year ? 1: -1;
});
console.table(ordered);

// Array.prototype.reduce()
// 4. How many years did all the inventors live?
const totalYears = inventors.reduce((total, inventor) => {
  return total + (inventor.passed - inventor.year);
  // the last parameter in reduce(), '0', is the initial value of total. If not provided, total will  be undefined.
}, 0);
console.log(totalYears);

// 5. Sort the inventors by years lived
const oldest = inventors.sort((a, b) => {
  const ageOfA = a.passed - a.year;
  const ageOfB = b.passed - b.year;
  return ageOfA > ageOfB ? 1 : -1;
}); 
console.table(oldest);

// 6. create a list of Boulevards in Paris that contain 'de' anywhere in the name
// https://en.wikipedia.org/wiki/Category:Boulevards_in_Paris
const category = document.querySelector('.mw-category');
// Select all the links inside the 'div' with the class 'mw-category'. Found using Chrome DevTools. querySelector() returns a node list, not an array, so we convert it to an array with Array.from()
// const links = Array.from(category.querySelectorAll('a'));
// console.log(links);

// This gives us just the text content inside that link
// const de = links.map(link => link.textContent).filter(streetName => streetName.includes('de'));

// Can be combined:
// const links = document.querySelector('.mw-category a');


// 7. sort Exercise
// Sort the people alphabetically by last name
const sortedLastNames = people.sort(function(a, b) {
  const [aLast, aFirst] = a.split(', ');
  const [bLast, bFirst] = b.split(', ');
  return aLast > bLast ? 1 : -1;
});

console.table(sortedLastNames);

// 8. Reduce Exercise
// Sum up the instances of each of these
const data = ['car', 'car', 'truck', 'truck', 'bike', 'walk', 'car', 'van', 'bike', 'walk', 'car', 'van', 'car', 'truck' ];

const transportation = data.reduce((obj, item) => {
  console.log(item);
  if (!obj[item]) { obj[item] = 0; }
  obj[item]++;
  return obj;
  // obj is initialized as an empty object
}, {});
console.log(transportation);

const people = [
  { name: 'Wes', year: 1988 },
  { name: 'Kait', year: 1986 },
  { name: 'Irv', year: 1970 },
  { name: 'Lux', year: 2015 }
];

const comments = [
  { text: 'Love this!', id: 523423 },
  { text: 'Super good', id: 823423 },
  { text: 'You are the best', id: 2039842 },
  { text: 'Ramen is my fav food ever', id: 123523 },
  { text: 'Nice Nice Nice!', id: 542328 }
];

// Some and Every Checks
// Array.prototype.some() // is at least one person 19 or older?
const isAdult = people.some((person) => {
  const currentYear = (new Date()).getFullYear();
  return currentYear - person.year >= 19;
});

// The above can be shortened to with arrow function and implicit return
const isAdult = people.some(person => 
                            (new Date()).getFullYear() - person.year >= 19);
// Should return true
console.log(isAdult);
console.log({isAdult}); // Shows you the variable name AND the value

// Array.prototype.every() // is everyone 19 or older?
const allAdults = people.every(person =>
                               (new Date()).getFullYear() - person.year >= 19);

console.log({allAdults}); // Should return false

// Array.prototype.find()
// Find is like filter, but instead returns just the one you are looking for
// find the comment with the ID of 823423
const comment = comments.find(comment => comment.id === 82423);
console.log({comment});

// Array.prototype.findIndex()
// Find the comment with this ID
// delete the comment with the ID of 823423
const index = comments.findIndex(comment => comment.id === 82423);
console.log(index); // Returns 1
comments.splice(index, 1); // Delete comment at index 1

// Creating a new array is preferred by the React community. If you don't use the spread operator, your new array will contain 2 arrays
const newComments = [
  // Copies elements from 0 to index (exclusive)
  ...comments.slice(0, index),
  // Copies elements from position index+1 to the end of the array 
  ...comments.slice(index+1) 
];

console.table(newComments);