Javascript 如何获取数组中的唯一值
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How to get unique values in an array
提问by Astronaut
How can I get a list of unique values in an array? Do I always have to use a second array or is there something similar to java's hashmap in JavaScript?
如何获取数组中唯一值的列表？我是否总是必须使用第二个数组，或者是否有类似于 JavaScript 中 java 的 hashmap 的东西？
I am going to be using JavaScriptand jQueryonly. No additional libraries can be used.
我将只使用JavaScript和jQuery。不能使用额外的库。
采纳答案by Hymanwanders
Since I went on about it in the comments for @Rocket's answer, I may as well provide an example that uses no libraries. This requires two new prototype functions, containsand unique
由于我在@Rocket 的回答的评论中继续讨论它，我不妨提供一个不使用库的示例。这需要两个新的原型函数，contains以及unique
Array.prototype.contains = function(v) {
for (var i = 0; i < this.length; i++) {
if (this[i] === v) return true;
}
return false;
};
Array.prototype.unique = function() {
var arr = [];
for (var i = 0; i < this.length; i++) {
if (!arr.contains(this[i])) {
arr.push(this[i]);
}
}
return arr;
}
var duplicates = [1, 3, 4, 2, 1, 2, 3, 8];
var uniques = duplicates.unique(); // result = [1,3,4,2,8]
console.log(uniques);For more reliability, you can replace containswith MDN's indexOfshim and check if each element's indexOfis equal to -1: documentation
为了获得更高的可靠性，您可以contains用 MDN 的indexOfshim替换并检查每个元素indexOf是否等于 -1：文档
回答by Josh Mc
Or for those looking for a one-liner (simple and functional), compatible with current browsers:
或者对于那些正在寻找与当前浏览器兼容的单线（简单且实用）的人：
let a = ["1", "1", "2", "3", "3", "1"];
let unique = a.filter((item, i, ar) => ar.indexOf(item) === i);
console.log(unique);Update 18-04-2017
更新 18-04-2017
It appears as though 'Array.prototype.includes' now has widespread support in the latest versions of the mainline browsers (compatibility)
似乎“Array.prototype.includes”现在在最新版本的主线浏览器中得到了广泛的支持（兼容性）
Update 29-07-2015:
2015 年 7 月 29 日更新：
There are plans in the works for browsers to support a standardized 'Array.prototype.includes' method, which although does not directly answer this question; is often related.
有计划让浏览器支持标准化的“Array.prototype.includes”方法，虽然它没有直接回答这个问题；往往是相关的。
Usage:
用法：
["1", "1", "2", "3", "3", "1"].includes("2"); // true
Pollyfill (browser support, source from mozilla):
Pollyfill（浏览器支持，来自 mozilla）：
// https://tc39.github.io/ecma262/#sec-array.prototype.includes
if (!Array.prototype.includes) {
Object.defineProperty(Array.prototype, 'includes', {
value: function(searchElement, fromIndex) {
// 1. Let O be ? ToObject(this value).
if (this == null) {
throw new TypeError('"this" is null or not defined');
}
var o = Object(this);
// 2. Let len be ? ToLength(? Get(O, "length")).
var len = o.length >>> 0;
// 3. If len is 0, return false.
if (len === 0) {
return false;
}
// 4. Let n be ? ToInteger(fromIndex).
// (If fromIndex is undefined, this step produces the value 0.)
var n = fromIndex | 0;
// 5. If n ≥ 0, then
// a. Let k be n.
// 6. Else n < 0,
// a. Let k be len + n.
// b. If k < 0, let k be 0.
var k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);
// 7. Repeat, while k < len
while (k < len) {
// a. Let elementK be the result of ? Get(O, ! ToString(k)).
// b. If SameValueZero(searchElement, elementK) is true, return true.
// c. Increase k by 1.
// NOTE: === provides the correct "SameValueZero" comparison needed here.
if (o[k] === searchElement) {
return true;
}
k++;
}
// 8. Return false
return false;
}
});
}
回答by Charles Clayton
Here's a much cleaner solution for ES6 that I see isn't included here. It uses the Setand the spread operator: ...
这是一个更简洁的 ES6 解决方案，我看到这里没有包含。它使用Set和扩展运算符：...
var a = [1, 1, 2];
[... new Set(a)]
Which returns [1, 2]
哪个返回 [1, 2]
回答by Vamsi
One Liner, Pure JavaScript
单行，纯 JavaScript
With ES6 syntax
使用 ES6 语法
list = list.filter((x, i, a) => a.indexOf(x) === i)
list = list.filter((x, i, a) => a.indexOf(x) === i)
x --> item in array
i --> index of item
a --> array reference, (in this case "list")
With ES5 syntax
使用 ES5 语法
list = list.filter(function (x, i, a) {
return a.indexOf(x) === i;
});
Browser Compatibility: IE9+
浏览器兼容性：IE9+
回答by Adeel Imran
Using EcmaScript 2016 you can simply do it like this.
使用 EcmaScript 2016，您可以简单地这样做。
var arr = ["a", "a", "b"];
var uniqueArray = Array.from(new Set(arr)); // Unique Array ['a', 'b'];
Sets are always unique, and using Array.from()you can convert a Set to an array. For reference have a look at the documentations.
集合总是唯一的，使用Array.from()您可以将集合转换为数组。作为参考，请查看文档。
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/fromhttps://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/来自https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects /放
回答by Rohit.007
Now in ES6 we can use the newly introduced ES6 function
现在在 ES6 中我们可以使用新引入的 ES6 函数
let items = [1,1,1,1,3,4,5,2,23,1,4,4,4,2,2,2]
let uniqueItems = Array.from(new Set(items))
OR by Array spread syntax on iterables
OR 通过可迭代对象上的数组展开语法
let items = [1,1,1,1,3,4,5,2,23,1,4,4,4,2,2,2];
let uniqueItems = [...new Set(items)];
It will return the unique result.
它将返回唯一的结果。
[1, 3, 4, 5, 2, 23]
回答by kennebec
If you want to leave the original array intact,
如果你想保持原数组不变，
you need a second array to contain the uniqe elements of the first-
您需要第二个数组来包含第一个数组的唯一元素-
Most browsers have Array.prototype.filter:
大多数浏览器都有Array.prototype.filter：
var unique= array1.filter(function(itm, i){
return array1.indexOf(itm)== i;
// returns true for only the first instance of itm
});
//if you need a 'shim':
Array.prototype.filter= Array.prototype.filter || function(fun, scope){
var T= this, A= [], i= 0, itm, L= T.length;
if(typeof fun== 'function'){
while(i<L){
if(i in T){
itm= T[i];
if(fun.call(scope, itm, i, T)) A[A.length]= itm;
}
++i;
}
}
return A;
}
Array.prototype.indexOf= Array.prototype.indexOf || function(what, i){
if(!i || typeof i!= 'number') i= 0;
var L= this.length;
while(i<L){
if(this[i]=== what) return i;
++i;
}
return -1;
}
回答by Fawntasia
These days, you can use ES6's Set data type to convert your array to a unique Set. Then, if you need to use array methods, you can turn it back into an Array:
现在，您可以使用 ES6 的 Set 数据类型将数组转换为唯一的 Set。然后，如果你需要使用数组方法，你可以把它变回一个数组：
var arr = ["a", "a", "b"];
var uniqueSet = new Set(arr); // {"a", "b"}
var uniqueArr = Array.from(uniqueSet); // ["a", "b"]
//Then continue to use array methods:
uniqueArr.join(", "); // "a, b"
回答by Calvin
回答by Rocket Hazmat
Using jQuery, here's an Array unique function I made:
使用 jQuery，这是我制作的 Array 独特功能：
Array.prototype.unique = function () {
var arr = this;
return $.grep(arr, function (v, i) {
return $.inArray(v, arr) === i;
});
}
console.log([1,2,3,1,2,3].unique()); // [1,2,3]
