JS数组去重的十种方法
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));
