Several ideas and implementation code summary of using javascript to deduplicate arrays

1. Array traversal method

The simplest method to remove duplicates, implementation idea: create a new array, traverse the incoming array, if the value is not in the new array, add it to the new array ; Note: The method "indexOf" to determine whether the value is in the array is an ECMAScript5 method. It is not supported below IE8. You need to write more code that is compatible with lower version browsers. The source code is as follows:

// 最简单数组去重法 
function unique1(array){ 
var n = []; //一个新的临时数组 
//遍历当前数组 
for(var i = 0; i < array.length; i++){ 
//如果当前数组的第i已经保存进了临时数组，那么跳过， 
//否则把当前项push到临时数组里面 
if (n.indexOf(array[i]) == -1) n.push(array[i]); 
} 
return n; 
}

2. Object key-value pairing method
This method executes faster than any other method, but it takes up more memory. Implementation idea: create a new js object and a new array, and traverse 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. Note: When determining whether it is a js object key, "toString()" will be automatically executed on the incoming key. Different keys may be mistaken for the same; for example: a[1], a["1"]. To solve the above problem, you still have to call "indexOf".

// 速度最快， 占空间最多（空间换时间） 
function unique2(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; 
}

3. Array subscript judgment method
You still have to call "indexOf". The performance is similar to method 1. Implementation idea: If the i-th of the current array If the first occurrence of an item in the current array is not i, then it means that the i-th item is repeated and will be ignored. 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; 
}

4. Adjacent removal method after sorting
Although the sorting result of the "sort" method of the native array is not very reliable, it does not pay attention to the order. This shortcoming has no effect in deduplication. Implementation idea: Sort the incoming array so that the same values ​​are adjacent after sorting, 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 unique4(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; 
}

5. Optimizing array traversal method
The implementation code of this method is quite cool. The implementation idea: get the rightmost value without duplication and put it in 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) Recommended

// 思路：获取没重复的最右一值放入新数组 
function unique5(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; 
}

Determine whether the browser supports indexOf, indexOf is ecmaScript5 The new method is not supported below IE8 (including IE8, IE8 only supports part of ecma5)

if (!Array.prototype.indexOf){ 
// 新增indexOf方法 
Array.prototype.indexOf = function(item){ 
var result = -1, a_item = null; 
if (this.length == 0){ 
return result; 
} 
for(var i = 0, len = this.length; i < len; i++){ 
a_item = this[i]; 
if (a_item === item){ 
result = i; 
break; 
} 
} 
return result; 
} 
}

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