es6 實現數組的操做

一、實現數組的去重：

　　1.一、方法一：

let arr = [{id: 1, name: 'aa'},  {id: 2, name: 'bb'}, {id: 3, name: 'cc'}, {id: 4, name: 'dd'}, {id: 5, name: 'ee'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}];

function unique(array) {
    const res = new Map();
    return array.filter((arr) => !res.has(arr.id) && res.set(arr.id, 1));   //用列表的id判斷是否有重複     
}

unique(arr);

　　1.二、方法二：

let hash = {},
     arr = [{id: 1, name: 'aa'},  {id: 2, name: 'bb'}, {id: 3, name: 'cc'}, {id: 4, name: 'dd'}, {id: 5, name: 'ee'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}, {id: 1, name: 'aa'}];

const newArr = arr.reduceRight((item, next) => {
    hash[next.id] ? '' : hash[next.id] = true && item.push(next);
    return item;
}, []);    console.log(newArr);

二、實現數組的過濾：

let arr = [{id: 1, name: 'aa'},  {id: 2, name: 'bb'}, {id: 3, name: 'cc'}, {id: 4, name: 'dd'}, {id: 5, name: 'ee'}];

function filter(arrayList, id) {
    let temp = arrayList.filter((list) => {
        if(list.id === id) {    //過濾列表id等於id值，相反也能夠用"!=="來過濾不等於id值的列表
            return list;
        }
    });
    return temp;
}

filter(arr, 1);　　

 三、數組的相同屬性值的合併:

let a = [{id: 1, name: 'a'}, {id: 2, name: 'b'}, {id: 1, name: 'c'},{id: 3, name: 'd'}, {id: 2, name: 'e'}, {id: 4, name: 'f'}];

let b = a.reduce((memo, {id, name}) => {
    !memo[id] ? memo[id] = name : memo[id] += name;
    return memo;
}, {});　　//{1: "ac", 2: "be", 3: "d", 4: "f"}

四、數組的扁平化：

function convert(val) {
    return val.reduce((init, next) => {
        if(typeof next === 'object') {
            next.forEach(item => {
                if(typeof item === 'object') {
                    init = init.concat(convert(item));
                } else {
                    init.push(item);
                }
            });
        } else {
            init.push(next);
        }
        return init;
    }, [])
}

Array.from(new Set(convert([1, 2, [3, 2, 1, [1, 2, 3, 4]]])));    //[1, 2, 3, 4]

五、摘取數組對象的某幾個字段：

var arr = [
  {
    'id': '1',
    'name': 'img1',
    'imgUrl': './img1.jpg',
  },
  {
    'id': '2',
    'name': 'img2',
    'imgUrl': './img2.jpg',
  },
  {
    'id': '3',
    'name': 'img3',
    'imgUrl': './img3.jpg',
  }
];
arr.map(x => {return {'imgUrl': x.imgUrl, 'name': x.name}}) 

 六、兩個數組拼接成對象數組：

　　方法一：

let metrodates = ['2008-01', '2008-02', '2008-03'];
let figures = [0, 0.555, 0.293];
let output = metrodates.map((date, i) =>({date, data: figures [i]})); 
console.log(output);    //[{date: "2008-01", data: 0}, {date: "2008-02", data: 0.555}, {date: "2008-03", data: 0.293}]

 　　方法二：

const zip = ([x, ...xs],  [y, ...ys]) => {
    if(x === undefined || y === undefined)
        return []; 
    else
        return [[x, y], ...zip(xs, ys)];
    }
let metrodates = ['2008-01', '2008-02', '2008-03'];
let figures = [0, 0.555, 0.293];
let output = zip(metrodates, figures).map(([date, data]) =>({date, data}));
console.log(output);   //[{date: "2008-01", data: 0}, {date: "2008-02", data: 0.555}, {date: "2008-03", data: 0.293}]

 　　方法三：

const isEmpty = xs => xs.length === 0;
const head =([x, ...xs]) => x;
const tail =([x, ...xs]) => xs;
const map = (f, ...xxs) => {
    let loop = (acc, xxs) => {
        if(xxs.some(isEmpty)) 
            return acc; 
        else
        return loop([...acc, f(...xxs.map(head))], xxs.map(tail));
    };
    return loop([], xxs);
}; 
let metrodates = ['2008-01', '2008-02', '2008-03'];
let figures = [0, 0.555, 0.293];
let output = map((date, data) =>({date, data}), metrodates, figures);
console.log(output);