如何在 JavaScript 中创建唯一项目列表? [英] How to create a list of unique items in JavaScript?

问题描述

在我的 CouchDB 缩减功能中，我需要将项目列表缩减为唯一的项目.

In my CouchDB reduce function I need to reduce a list of items to the unique ones.

注意:在这种情况下，可以有一个列表，它将是少数字符串类型的项目.

我目前的方法是设置一个对象的键，然后返回那个对象的键因为代码不能使用诸如 _.uniq 之类的东西.

My current way is to set keys of a object, then return the keys of that object since the place the code can't use things like _.uniq for example.

我想找到比这更优雅的拼写方式.

I'd like to find a more elegant way to spell it than this.

function(keys, values, rereduce) {
  // values is a Array of Arrays
  values = Array.concat.apply(null, values);
  var uniq = {};
  values.forEach(function(item) { uniq[item] = true; });
  return Object.keys(uniq);
}

推荐答案

通常，您使用的方法是一个好主意.但我可以提出一个解决方案，让算法更快.

Commonly, the approach you used is a good idea. But I could propose a solution that will make the algorithm a lot faster.

function unique(arr) {
    var u = {}, a = [];
    for(var i = 0, l = arr.length; i < l; ++i){
        if(!u.hasOwnProperty(arr[i])) {
            a.push(arr[i]);
            u[arr[i]] = 1;
        }
    }
    return a;
}

如您所见，我们这里只有一个循环.

As you can see we have only one loop here.

我制作了一个 示例，用于测试您和我的解决方案.试试看吧.

I've made an example that is testing both your and my solutions. Try to play with it.

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