一、前言：

我们在实际工作中，或者在面试找工作时，都会用到或者被问到一个问题，那就是“数组如何去重”。是的，这个问题有很多种解决方案，看看下面的十种方式吧！

二、数组去重方式大汇总：

Methods 1: 思路：定义一个新数组，并存放原数组的第一个元素，然后将元素组一一和新数组的元素对比，若不同则存放在新数组中。

function unique(arr){ var res = [arr[0]]; for(var i=1; i<arr.length; i++){ var repeat = false; for(var j=0; j<res.length; j++){ if(arr[i] === res[j]){ repeat = true; break; } } if(!repeat){ res.push(arr[i]); } } return res;}console.log('------------方法一---------------');console.log(unique([1,1,2,3,5,3,1,5,6,7,4]));

Methods 2: 思路：先将原数组排序，在与相邻的进行比较，如果不同则存入新数组。

function unique2(arr){ var arr2 = arr.sort(); var res = [arr2[0]]; for(var i=1; i<arr2.length; i++){ if(arr2[i] !== res[res.length-1]){ res.push(arr2[i]); } } return res;}console.log('------------方法二---------------');console.log(unique2([1,1,2,3,5,3,1,5,6,7,4]));

Methods 3: 利用对象属性存在的特性，如果没有该属性则存入新数组。

function unique3(arr){ var res = []; var obj = {}; for(var i=0; i<arr.length; i++){ if( !obj[arr[i]] ){ obj[arr[i]] = 1; res.push(arr[i]); } } return res;}console.log('------------方法三---------------');console.log(unique3([1,1,2,3,5,3,1,5,6,7,4]));

Methods 4:利用数组的indexOf下标属性来查询。

function unique4(arr){ var res = []; for(var i=0; i<arr.length; i++){ if(res.indexOf(arr[i]) == -1){ res.push(arr[i]); } } return res;}console.log('------------方法四---------------');console.log(unique4([1,1,2,3,5,3,1,5,6,7,4]));

Methods 5: 利用数组原型对象上的includes方法。

function unique5(arr){ var res = []; for(var i=0; i<arr.length; i++){ if( !res.includes(arr[i]) ){ // 如果res新数组包含当前循环item res.push(arr[i]); } } return res;}console.log('------------方法五---------------');console.log(unique5([1,1,2,3,5,3,1,5,6,7,4]));

Methods 6: 利用数组原型对象上的 filter 和 includes方法。

function unique6(arr){ var res = []; res = arr.filter(function(item){ return res.includes(item) ? '' : res.push(item); }); return res;}console.log('------------方法六---------------');console.log(unique6([1,1,2,3,5,3,1,5,6,7,4]));

Methods 7: 利用数组原型对象上的 forEach 和 includes方法。

function unique7(arr){ var res = []; arr.forEach(function(item){ res.includes(item) ? '' : res.push(item); }); return res;}console.log('------------方法七---------------');console.log(unique7([1,1,2,3,5,3,1,5,6,7,4]));

Methods 8: 利用数组原型对象上的 splice 方法。

function unique8(arr){ var 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;}console.log('------------方法八---------------');console.log(unique8([1,1,2,3,5,3,1,5,6,7,4]));

Methods 9: 利用数组原型对象上的 lastIndexOf 方法。

function unique9(arr){ var res = []; for(var i=0; i<arr.length; i++){ res.lastIndexOf(arr[i]) !== -1 ? '' : res.push(arr[i]); } return res;}console.log('------------方法九---------------');console.log(unique9([1,1,2,3,5,3,1,5,6,7,4]));

Methods 10: 利用 ES6的set 方法。

function unique10(arr){ //Set数据结构，它类似于数组，其成员的值都是唯一的 return Array.from(new Set(arr)); // 利用Array.from将Set结构转换成数组}console.log('------------方法十---------------');console.log(unique10([1,1,2,3,5,3,1,5,6,7,4]));

三、其他：

有意思的是，当我把数组的长度变得很大的时候（如下所示），测试了一下不同方法的执行时间长短，会发现方法三、四、五、六、七相对来说会更有优势，而方法八的执行速度似乎一直垫底。你也可以在你本地跑一下试试！

//测试用的超大数组
var arr = 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//这里只是举例方法三（如果你把所有方法放在一起测试，会更直观的看到执行时间的差异）

var time3 = new Date().getTime();function unique3(arr){ var res = []; var obj = {}; for(var i=0; i<arr.length; i++){ if( !obj[arr[i]] ){ obj[arr[i]] = 1; res.push(arr[i]); } } return res;}console.log('------------方法三---------------');console.log( unique3(arr) );console.log('3所花时间： ' + (new Date().getTime() - time3));

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