这篇文章主要介绍了JavaScript数组去重的十种方法,利用元素的属性和特性进行不同的去重方法,并实例演示如何测试去重超大数组,具体操作步骤大家可查看下文的详细讲解,感兴趣的小伙伴们可以参考一下。
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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