好像不是最全的数组去重方法

Posted 2021-02-01 qixidi

这一篇文章，我们讲解一下数组去重。

1.最简单粗暴地方式，两重for循环

let arr = [9, 5, 6, 5, ‘1‘, ‘1‘, true, 5, true];
for (var i = 0; i < arr.length; i++) {
    for (var j = i + 1; j < arr.length; j++) {
        if(arr[i] === arr[j]){
            arr.splice(j,1);
        }       
    }
}
console.log(arr); // [9, 5, 6, "1", true, undefined, null, NaN, NaN, {…}, {…}]
// 两个NaN, 因为NaN!=NaN

2.indexOf

let a = [];
for (var i = 0; i < arr.length; i++) {
    if(a.indexOf(arr[i]) === -1){
        a.push(arr[i]);
    }
}
console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, NaN, {…}, {…}]
// 两个NaN, 因为NaN!=NaN

3.includes

for (var i = 0; i < arr.length; i++) {
    if(!a.includes(arr[i])){
        a.push(arr[i]);
    }
}
console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, {…}, {…}]

4.Set

let a = [...(new Set(arr))];
console.log(a); // [9, 5, 6, "1", true, undefined, null, NaN, {…}, {…}]

5.filter

let a = arr.filter(function(value, index){
    return arr.indexOf(value, 0) === index;
})
console.log(a);// [9, 5, 6, "1", true, undefined, null, {…}, {…}]
arr.filter(function(value){
    return a.indexOf(value) === -1 ? a.push(value) : a;
})
console.log(a);// [9, 5, 6, "1", true, undefined, null, NaN, NaN, {…}, {…}]

6.sort

arr = arr.sort(); // 排序，如果相同就会挨着
a.push(arr[0]); // 先放数组第一个元素
for (var i = 1; i < arr.length; i++) {
    if(arr[i] !== arr[i - 1]){
        a.push(arr[i]);
    }
}

7.reduce

arr = arr.sort(); 
arr.reduce(function(preVal, nowVal){
    if(preVal !== nowVal){
        a.push(preVal);
    }
    return nowVal;
}, a)
arr.reduce(function(preVal, nowVal){
    return a.indexOf(nowVal) === -1 ? a.push(nowVal) : a;
}, a)
console.log(a); //["1", 5, 6, 9, NaN, NaN, {…}, {…}, null, true, undefined]

8.hasOwnProperty

let obj = {};
for (var i = 0; i < arr.length; i++) {
    if(!obj.hasOwnProperty(obj[typeof arr[i] + arr[i]])){
        obj[typeof arr[i] + arr[i]] = arr[i];
    }
}
console.log(Object.values(obj)); //[9, 5, 6, "1", true, undefined, null, NaN, {…}] 无法判断对象

9.对象数组去重方法

let obj = {};
for (var i = 0; i < arr.length; i++) {
    if(!obj[typeof arr[i] + arr[i]]){
        obj[typeof arr[i] + arr[i]] = arr[i];
    }
}
console.log(Object.values(obj)); //[9, 5, 6, "1", true, undefined, null, NaN, {…}]

10.Map

let map = new Map();
for (var i = 0; i < arr.length; i++) {
    if(!map.get(arr[i])){
        map.set(arr[i], arr[i]);
    }
}
console.log(map);

• 补充

我想说一下forEach与map

arr.forEach( function(element, index) {
    console.log(element);
});
arr.map(function(element, index){
    console.log(element);
});

• 相同点

  • 他们都是用来遍历数组的。

• 不同点

  • map能有返回值，forEach没有返回值。
  ``` let arr = [9,3,6,3,6,3]; arr = arr.forEach( function(element, index) { return element + 1; }); console.log(arr); // undefined arr = arr.map(function(element, index){ return element + 1; }); console.log(arr); //[10, 4, 7, 4, 7, 4] ```
  • forEach不能中途打断
  ``` let arr = [9,3,6,3,6,3]; arr.forEach( function(element, index) { console.log(element); if(index === 2){ return; //没用，break,continue会报错是无效的 } }); ```

• forEach模拟实现

  ``` Array.prototype.bforEach = function (fn) { let array = this; for (var i = 0; i < array.length; i++) { fn(array[i], i, array); } } arr.bforEach(function(element, index){ console.log(element); // 9, 3, 6, 3, 6, 3 }); ```

• map模拟实现

  ``` Array.prototype.Map = function (fn) { let array = this, a = [], r; for (var i = 0; i < array.length; i++) { r = fn(array[i], i, array); a.push(r); } return a; } ```

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来源：https://segmentfault.com/a/1190000017764436