JavaScript 04 — Array Cardio Day 1

实现效果

熟悉数组的各种方法：filter()、map()、sort()、reduce()。

<script>
// Get your shorts on - this is an array workout!
// ## Array Cardio Day 1

// Some data we can work with

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

// Array.prototype.filter()
// 1. Filter the list of inventors for those who were born in the 1500's
let fifteen = inventors.filter(inventor => (
  inventor.year >= 1500 && inventor.year < 1600
))
console.log(fifteen);

// Array.prototype.map()
// 2. Give us an array of the inventors first and last names
let fullnames = inventors.map(inventor => (inventor.first + inventor.last))
console.log(fullnames);

// Array.prototype.sort()
// 3. Sort the inventors by birthdate, oldest to youngest
let ordered = inventors.sort((a, b) => a.year > b.year)
console.log(ordered);

// Array.prototype.reduce()
// 4. How many years did all the inventors live all together?
let alllive = inventors.reduce((acc, inventor) => {
  return acc + (inventor.passed - inventor.year)
}, 0)
console.log(alllive);


// 5. Sort the inventors by years lived
let oldest = inventors.sort((a, b) => {
  let old = a.passed - a.year
  let young = b.passed - b.year
  return old > young ? -1 : 1
})
console.log(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

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

// 8. Reduce Exercise
// 计算数组中每个元素出现的次数 https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
// 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 transport = data.reduce((acc, item) => {
  //两个参数  1。回调函数4个参数 1累加器累计的返回值 2处理的当前元素   2。作为第一次调用reduce的初始值

  // if (acc.indexOf(item) === -1) {
  //   acc.push(item)
  // }
  // return acc

  // if (!acc[item]) {
  //   acc[item] = 0
  // }
  // acc[item]++
  // return acc

  if (item in acc) {
    acc[item]++
  } else {
    acc[item] = 1
  }
  return acc
}, [])
console.log(transport);
  </script>