Data Processing

資料處理

  • 下列程式碼簡介

    • filter 用法，It get a function to do something

    • map 用法，It get an array and output an array, the array.length will NOT change

    • sort 用法

    • reduce 用法

    • 加減數字後，再排序

    • 處理字串後（split），再排序

    • reduce：計算各項目出現的次數，實用必看

  • // Source: https://github.com/wesbos/JavaScript30

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()
// Me: It get a function to do something.
// 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));

console.table(fifteen);
/* Before Optimization
const fifteen = invertors.filter(function(inventor) {
  if(inventor.year >= 1500 && inventor.year < 1600)
    return true;
}); //And it no need to "else return false"
*/

// Array.prototype.map()
// Me: It get an array and output an array, the array.length will NOT change.
// 2. Give us an array of the inventor first and last names
const fullNames = inventors.map(inventor => `${inventor.first} ${inventor.last}`);
console.log(fullNames);

/* Before Optimazation
const fullNames = inventors.map(inventor => inventors.frst + ' ' + inventor.last);
*/

// 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;
//   }
// });

const ordered = inventors.sort((a, b) => 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);
}, 0); // 0 is for set total from a UNDEFINED to a number.

console.log(totalYears);

/* The Old days without reduce
var totalYears = 0;
for (var i = 0; i < inventors.length; i++) {
  totalYears += inventors[i].passed - inventors[i].year;
}
*/

// 5. Sort the inventors by years lived
const oldest = inventors.sort(function(a, b) {
  const lastInventor = a.passed - a.year;
  const nextInventor = b.passed - b.year;
  return lastInventor > nextInventor ? -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');
// Change a NodeList to an Array!!
// Also can: const links = [...category.querySelectorAll('a')];
// const links = Array.from(category.querySelectorAll('a'));
// const de = links
//             .map(link => link.textContent)
//             .filter(streetName => streetName.includes('de'));

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

// 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', 'pogostick'];

const transportation = data.reduce(function(obj, item) {
  if (!obj[item]) {
    obj[item] = 0; // Set the initial value.
  }
  obj[item]++;
  return obj;
}, {}); // Start with a empty object.

console.log(transportation);

  • 下列程式碼簡介

    • some 的用法

    • find 的用法

    • findIndex 的用法

    • .splice(index, 1)：刪除 array 的某一項

    • Redux 刪除 array 的某一項的作法

  • // Source: https://github.com/wesbos/JavaScript30

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?
// const isAdult = people.some(function(person) {
//   const currentYear = (new Date()).getFullYear();
//   if(currentYear - person.year >= 19) {
//     return true;
//   }
// });

const isAdult = people.some(person => ((new Date()).getFullYear()) - person.year >= 19);

console.log({isAdult}); //  curly brackets 只是讓它變成 Object 而已，沒啥特別意思

// Array.prototype.every() // is everyone 19?

const allAdults = people.every(person => ((new Date()).getFullYear()) - person.year >= 19);
console.log({allAdults});

// Array.prototype.find()
// Find is like filter, but instead returns just the one you are looking for
// 很像 filter，但 filter 回傳的是 array 的 subset，find 回傳的是找到的第一項
// find the comment with the ID of 823423

// const comment = commnets.find(function(commnet){
//   if (comment.id === '823423'){
//     return true;
//   }
// });

const comment = comments.find(comment => comment.id === 823423);

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 === 823423);
console.log(index);

// comments.splice(index, 1); 刪除 array 的某一項

// Redux 的作法，複製一個新的。記得要 ... spread 才會是預期中的 array
const newComments = [
  ...comments.slice(0, index),
  ...comments.slice(index + 1)
];

  • 下列程式碼簡介

    • 多種複製 Array 與 Object 的方式，實用必看

  • // Source: https://github.com/wesbos/JavaScript30

// start with strings, numbers and booleans
// let age = 100;
// let age2 = age;
// console.log(age, age2); // 100, 100
// age = 200;
// console.log(age, age2); // 200, 100

// let name = 'Wes';
// let name2 = name;
// console.log(name, name2); // Wes, Wes
// name = 'wesley';
// console.log(name, name2); // wesley, Wes

// Let's say we have an array
const players = ['Wes', 'Sarah', 'Ryan', 'Poppy'];

// and we want to make a copy of it.
const team = players;

console.log(players, team);
// You might think we can just do something like this:
// team[3] = 'Lux';

// however what happens when we update that array?

// now here is the problem!

// oh no - we have edited the original array too!

// Why? It's because that is an array reference, not an array copy. They both point to the same array!
// 因為 Array 的複製不是你想像的複製，它只是 reference 到同一個東西
// 所以你改了你新增的變數，會直接改到原始的變數！
// 替代的 copy 方法如下～
// So, how do we fix this? We take a copy instead!
const team2 = players.slice();　// 方法一

// one day

// or create a new array and concat the old one in
const team3 = [].concat(players); // 方法二

// or use the new ES6 Spread
const team4 = [...players]; // 方法三：ES6 作法 作者prefer
team4[3] = 'heeee hawww';
console.log(team4);

const team5 = Array.from(players); // 方法四：（有點記不起來）作者prefer

// now when we update it, the original one isn't changed

// The same thing goes for objects, let's say we have a person object

// with Objects
const person = {
  name: 'Wes Bos',
  age: 80
};

// and think we make a copy:
// const captain = person;
// captain.number = 99;

// how do we take a copy instead?
const cap2 = Object.assign({}, person, { number: 99, age: 12 }); // 方法一
console.log(cap2);

// We will hopefully soon see the object ...spread
// const cap3 = {...person};

// Things to note - this is only 1 level deep - both for Arrays and Objects. lodash has a cloneDeep method, but you should think twice before using it.

const wes = {
  name: 'Wes',
  age: 100,
  social: {
    twitter: '@wesbos',
    facebook: 'wesbos.developer'
  }
};

console.clear();
console.log(wes);

const dev = Object.assign({}, wes); // 提醒：.assign 的複製只有一層！
                                    // 所以改了 dev.social.twitter = ooxx 的話，
                                    // 會改到原本的 wes Object

const dev2 = JSON.parse(JSON.stringify(wes)); // 窮人的 deep clone。 作者不喜歡這作法～
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