Detailed explanation of js array deduplication and deflattening-JS Tutorial-php.cn

Detailed explanation of js array deduplication and deflattening

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Release： 2018-03-07 11:33:42

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This article mainly shares with you the detailed explanation of js array deduplication and deflattening, hoping it can help everyone.

Array deduplication

var arr = [1, 43, 4, 3, 2, 4, 3];
// After removing duplicates
arr = [1, 43, 4, 3, 2]

Traditional method, for loop implementation

function dedupe(arr) {
    var rets = [];    for (var i = 0; i < arr.length; i ++) {        if (!rets.includes(arr[i])) {
            rets.push(arr[i]);
        }
    }    return rets;
}// 方法二: forEach方法实现function dedupe(arr) {
    var rets = [];
    arr && arr.forEach(function(item){
        if (!rets.includes(item)){
            rets.push(item);
        }
    });    return rets;
}

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ES6 method implementation

// es6提供的新的数据结构Set，类似数组，但是成员的值都是唯一的，没有重复的值。function dedupe(arr) {
    var newSet = new Set(arr);  // arr变成了set的数据结构，并去除了其中重复的元素
    return Array.from(newSet);  // Array.from方法将set数据结构转为数组数据结构}

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Array deflattening
The flattening of an array is to convert a multi-layered array array (the nesting can be any number of layers) into an array with only one layer

var arr = [1, 2, 3, [4, 3, [2, 7], 2], 5, [5, 9, 10], 7];
// After de-flattening
arr = [1, 2, 3, 4, 3, 2, 7, 2, 5, 5, 9, 10, 7];

(1) Loop recursion implementation

// for循环，如果子元素还是数组，则递归调用该方法function flatten(arr) {
    var rets = [];    for(var i = 0; i < arr.length; i ++) {        if (Array.isArray(arr[i])) {
            rets = rets.concat(flatten(arr[i]));
        } else {
            rets.push(arr[i]);
        }
    }    return rets;
}// 使用forEachfunction flatten(arr) {
    var rets = [];
    arr && arr.forEach(function(item) => {
        if (Array.isArray(item)) {
            rets = rets.concat(flatten(item));
        } else {
            rets.push(item);
        }
    });    return rets;
}

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(2) Use reduce to simplify the code

function flatten(arr) {
    arr.reduce(function(pre, item){
        return pre.concat(Array.isArray(item) ? flatten(item) : item);
    }, [])
}

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(3) If the array elements are all numbers, you can use the toString method

function flatten(arr) {
    var newArr = arr.toString().split(&#39;,&#39;);    return newArr.map(function(item){
        return +item;        // 将字符串转为数字
    });
}

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