Summary of JS array deduplication methods

This article mainly shares with you a summary of JS array deduplication methods. There are seven methods in total. I hope it can help everyone.

The easiest way:

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var arr=[2,8,5,0,5,2,6,7,2];function unique1(arr){ var hash=[]; for (var i = 0; i if(hash.indexOf(arr[i])==-1){ hash.push(arr[i]); } } return hash; }

Method 1:

Double-layer loop, outer loop element, inner loop comparison value

If there is If the values ​​are the same, they will be skipped. If they are not the same, they will be pushed into the array.

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

Double-layer loop, outer loop element, inner loop comparison value

When the values ​​are the same, delete this value

Note: After deleting the element, you need to reduce the length of the array by 1.

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Array.prototype.distinct = function(){ var arr = this, result = [], i, j, len = arr.length; for(i = 0; i for(j = i + 1; 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(); //Return [3,4,2,1]

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Array.prototype.distinct = function (){ var arr = this, i, j, len = arr.length; for(i = 0; i for(j = i + 1; 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

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

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Array.prototype.distinct = function (){ var arr = this, i, obj = {}, result = [], len = arr.length; for(i = 0; i if(!obj[arr[i]]){ //If it can be found, it proves that the array elements are repeated 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

Method 4: Recursive deduplication of arrays

Use the recursive idea

Sort first, and then compare from the end, if you encounter the same , then delete

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Array.prototype.distinct = function (){ var arr = this, len = arr.length; arr.sort(function(a,b){ //Sort the array to facilitate comparison return a - b; }) function loop(index){ if(index >= 1){ if(arr[index] === arr[index-1]){ arr.splice(index,1); } loop(index - 1); //Recursive loop function to remove duplicates } } 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

Method Five: Using indexOf and forEach

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Array.prototype.distinct = function (){ var arr = this, result = [], len = arr.length; arr.forEach(function(v, i ,arr){ //Use map and filter here The method can also be implemented var bool = arr.indexOf(v,i+1); // Start looking for duplicates from the next index value of the incoming parameter 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

Method 6: Use ES6's set

Set data structure, which 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

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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 the for...of loop internally

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

The following is a supplementary introduction to the method of merging arrays and removing duplicates

##1. concat() method

Idea: The concat() method combines the incoming array or non-array value with the original array to form a new array and returns it. This method will generate a new array.

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function concatArr(arr1, arr2){ ##var arr = arr1.concat (arr2); arr = unique1(arr);//Refer to any of the above deduplication methods return arr; }

2. Array.prototype.push.apply()

Idea: The advantage of this method is that it does not generate a new array.

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var a = [1, 2, 3]; var b = [4, 5, 6]; Array.prototype.push.apply(a, b);//a=[1,2,3,4,5,6] //等效于:a.push.apply(a, b); //Also equivalent to [].push.apply(a, b); function concatArray(arr1,arr2){ Array.prototype.push.apply(arr1, arr2); arr1 = unique1(arr1); return arr1;

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