Summary of several methods to achieve array deduplication in js-JS Tutorial-php.cn

Summary of several methods to achieve array deduplication in js

巴扎黑

Release： 2017-07-18 18:24:07

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Method 1:

Double-layer loop, outer loop element, compare value when inner loop
If there is the same value If it is different, it will be pushed into the array.

Array.prototype.distinct = function(){var arr = this,
        result = [],
        i,
        j,
        len = arr.length;for(i = 0; i < len; i++){for(j = i + 1; j < len; j++){if(arr[i] === arr[j]){
                j = ++i;
            }
        }
        result.push(arr[i]);
    }return result;
}var arra = [1,2,3,4,4,1,1,2,1,1,1];
arra.distinct();             //返回[3,4,2,1]

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Method 2: Use splice to operate directly on the original array

Double-layer loop, outer loop element, compare value when inner loop
If the value is the same, delete this value

Notes: After deleting elements, you need to reduce the length of the array by 1.

Array.prototype.distinct = function (){var arr = this,
        i,
        j,
        len = arr.length;for(i = 0; i < len; i++){for(j = i + 1; j < len; j++){if(arr[i] == arr[j]){
                arr.splice(j,1);
                len--;
                j--;
            }
        }
    }return arr;
};var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,];var b = a.distinct();
console.log(b.toString()); //1,2,3,4,5,6,56

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Advantages: Simple and easy to understand
Disadvantages: High memory usage and slow speed

Method 3: Use the properties of objects that cannot be the same to deduplicate

Array.prototype.distinct = function (){var arr = this,
        i,
        obj = {},
        result = [],
        len = arr.length;for(i = 0; i< arr.length; i++){if(!obj[arr[i]]){    //如果能查找到，证明数组元素重复了obj[arr[i]] = 1;
            result.push(arr[i]);
        }
    }return result;
};var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,];var b = a.distinct();
console.log(b.toString()); //1,2,3,4,5,6,56

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Method 4: Array recursion Remove duplicates

Use recursive thinking
Sort first, then compare from the end, if they are the same, delete

Array.prototype.distinct = function (){var arr = this,
        len = arr.length;

    arr.sort(function(a,b){        //对数组进行排序才能方便比较return a - b;
    })function loop(index){if(index >= 1){if(arr[index] === arr[index-1]){
                arr.splice(index,1);
            }
            loop(index - 1);    //递归loop函数进行去重        }
    }
    loop(len-1);return arr;
};var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,56,45,56];var b = a.distinct();
console.log(b.toString());        //1,2,3,4,5,6,45,56

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Method 5: Using `indexOf` and `forEach`

Array.prototype.distinct = function (){var arr = this,
        result = [],
        len = arr.length;

    arr.forEach(function(v, i ,arr){        //这里利用map，filter方法也可以实现var bool =  arr.indexOf(v,i+1);        //从传入参数的下一个索引值开始寻找是否存在重复if(bool === -1){
            result.push(v);
        }
    })return result;
};var a = [1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,3,3,3,3,3,3,3,2,3,3,2,2,1,23,1,23,2,3,2,3,2,3];var b = a.distinct();
console.log(b.toString());    //1,23,2,3

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Method 6: Using ES6's set

Set data structure is similar to an array, and the values of its members are all unique.

Use Array.from to convert the Set structure into an array

function dedupe(array){return Array.from(new Set(array));
}

dedupe([1,1,2,3]) //[1,2,3]

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The expansion operator (...) uses for internally. ..of loop

let arr = [1,2,3,3];
let resultarr = [...new Set(arr)];   
console.log(resultarr);  //[1,2,3]

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