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Remove duplicate data from JS array

小云云
小云云Original
2018-03-13 16:08:191600browse

In JS, we often encounter the need to remove duplicate data from arrays. Here we introduce four algorithms to achieve the function of deduplicating JS arrays. I hope it can help everyone.

1. The fastest algorithm: object key-value pair method

Implementation idea: create a new js object and a new array, and when traversing the incoming array, determine whether the value is a js object key, if not, add the key to the object and put it into a new array.

//注意点: 判断 是否为js对象键时,会自动对传入的键执行“toString()”,不同的键可能会被误认为一样;例如: a[1]、a["1"] 。解决上述问题还是得调用“indexOf”。
        //速度最快, 占空间最多(空间换时间)
        function unique(array){
            var n = {}, r = [], len = array.length, val, type;
            for (var i = 0; i < array.length; i++) {                val = array[i];                type = typeof val;                if (!n[val]) {
                    n[val] = [type];
                    r.push(val);
                } else if (n[val].indexOf(type) < 0) {
                    n[val].push(type);
                    r.push(val);
                }
            }            return r;
        }

2. The most ingenious algorithm: optimized array traversal method

Implementation idea: get the rightmost value without repetition and put it into a new array. (When duplicate values ​​are detected, the current loop is terminated and the next round of judgment of the top-level loop is entered)

function unique1(array){
            var r = [];            for(var i = 0, l = array.length; i<l; i++){                for(var j = i + 1; j < l; j++)                    if(array[i] == array[j]) j == ++i;
                r.push(array[i]);
            }            return r;
        }

3. Algorithm: adjacent removal method after sorting

Implementation idea: pass in the array Sort, after sorting, the same values ​​are adjacent, and then when traversing, only add values ​​that are not duplicates of the previous value to the new array.

//将相同的值相邻,然后遍历去除重复值
        function unique2(array){
            array.sort();            var re=[array[0]];            for(var i = 1; i < array.length; i++){                if( array[i] !== re[re.length-1])
                {
                    re.push(array[i]);
                }
            }            return re;
        }

4. Algorithm: Array Subscript Judgment Method

Implementation idea: If the i-th item of the current array first appears in a position other than i in the current array, then it means the i-th item It's a duplicate, so ignore it. Otherwise, store the result array

function unique3(array){
            var n = [array[0]]; //结果数组
            //从第二项开始遍历
            for(var i = 1; i < array.length; i++) {                //如果当前数组的第i项在当前数组中第一次出现的位置不是i,
                //那么表示第i项是重复的,忽略掉。否则存入结果数组
                if (array.indexOf(array[i]) == i) n.push(array[i]);
            }            return n;
        }

                                                                                                                                                 

In JS, we often encounter the need to remove duplicate data in arrays. Here we introduce four algorithms to achieve the function of deduplicating JS arrays.

1. The fastest algorithm: object key-value pairing method

Implementation idea: Create a new js object and a new array. When traversing the incoming array, determine whether the value is the key of the js object. If not, Add the key to the object and put it into a new array.

//注意点: 判断 是否为js对象键时,会自动对传入的键执行“toString()”,不同的键可能会被误认为一样;例如: a[1]、a["1"] 。解决上述问题还是得调用“indexOf”。
        //速度最快, 占空间最多(空间换时间)
        function unique(array){
            var n = {}, r = [], len = array.length, val, type;
            for (var i = 0; i < array.length; i++) {                val = array[i];                type = typeof val;                if (!n[val]) {
                    n[val] = [type];
                    r.push(val);
                } else if (n[val].indexOf(type) < 0) {
                    n[val].push(type);
                    r.push(val);
                }
            }            return r;
        }

2. The most ingenious algorithm: optimized array traversal method

Implementation idea: get the rightmost value without repetition and put it into a new array. (When duplicate values ​​are detected, the current loop is terminated and the next round of judgment of the top-level loop is entered)

function unique1(array){
            var r = [];            for(var i = 0, l = array.length; i<l; i++){                for(var j = i + 1; j < l; j++)                    if(array[i] == array[j]) j == ++i;
                r.push(array[i]);
            }            return r;
        }

3. Algorithm: adjacent removal method after sorting

Implementation idea: pass in the array Sort, after sorting, the same values ​​are adjacent, and then when traversing, only add values ​​that are not duplicates of the previous value to the new array.

//将相同的值相邻,然后遍历去除重复值
        function unique2(array){
            array.sort();            var re=[array[0]];            for(var i = 1; i < array.length; i++){                if( array[i] !== re[re.length-1])
                {
                    re.push(array[i]);
                }
            }            return re;
        }

4. Algorithm: Array Subscript Judgment Method

Implementation idea: If the i-th item of the current array first appears in a position other than i in the current array, then it means the i-th item It's a duplicate, so ignore it. Otherwise, store the result array

function unique3(array){
            var n = [array[0]]; //结果数组
            //从第二项开始遍历
            for(var i = 1; i < array.length; i++) {                //如果当前数组的第i项在当前数组中第一次出现的位置不是i,
                //那么表示第i项是重复的,忽略掉。否则存入结果数组
                if (array.indexOf(array[i]) == i) n.push(array[i]);
            }            return n;
        }

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