史上最全JavaScript數(shù)組去重的十種方法（推薦）
一、前言：
我們?cè)趯?shí)際工作中，或者在面試找工作時(shí)，都會(huì)用到或者被問(wèn)到一個(gè)問(wèn)題，那就是“數(shù)組如何去重”。是的，這個(gè)問(wèn)題有很多種解決方案，看看下面的十種方式吧！
二、數(shù)組去重方式大匯總：
Methods 1: 思路：定義一個(gè)新數(shù)組，并存放原數(shù)組的第一個(gè)元素，然后將元素組一一和新數(shù)組的元素對(duì)比，若不同則存放在新數(shù)組中。
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：先將原數(shù)組排序，在與相鄰的進(jìn)行比較，如果不同則存入新數(shù)組。
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: 利用對(duì)象屬性存在的特性，如果沒(méi)有該屬性則存入新數(shù)組。
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: 利用數(shù)組的indexOf下標(biāo)屬性來(lái)查詢。
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: 利用數(shù)組原型對(duì)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新數(shù)組包含當(dāng)前循環(huán)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: 利用數(shù)組原型對(duì)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: 利用數(shù)組原型對(duì)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: 利用數(shù)組原型對(duì)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: 利用數(shù)組原型對(duì)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數(shù)據(jù)結(jié)構(gòu)，它類似于數(shù)組，其成員的值都是唯一的
return Array.from(new Set(arr)); // 利用Array.from將Set結(jié)構(gòu)轉(zhuǎn)換成數(shù)組
}
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，當(dāng)我把數(shù)組的長(zhǎng)度變得很大的時(shí)候（如下所示），測(cè)試了一下不同方法的執(zhí)行時(shí)間長(zhǎng)短，會(huì)發(fā)現(xiàn)方法三、四、五、六、七相對(duì)來(lái)說(shuō)會(huì)更有優(yōu)勢(shì)，而方法八的執(zhí)行速度似乎一直墊底。你也可以在你本地跑一下試試！
//測(cè)試用的超大數(shù)組
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//這里只是舉例方法三（如果你把所有方法放在一起測(cè)試，會(huì)更直觀的看到執(zhí)行時(shí)間的差異）
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所花時(shí)間： ' + (new Date().getTime() - time3));
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