过滤对象数组的最佳方法答案

【问题标题】：Best way to filter the array of objects过滤对象数组的最佳方法
【发布时间】：2019-02-09 16:36:54
【问题描述】：

我有一个对象数组，其中包含一个我想要过滤的名为“Country”的属性。我让用户选择他们想要查看的国家/地区并希望返回由该属性过滤的对象数组。完成此过程的最有效方法是什么？

  var countries = [{GINI: 56.2, Country: "Central African Republic", Values: Array, Date: "2008"},
  {GINI: 51.3, Country: "Brazil", Values: Array, Date: "2015"},{GINI: 51.1, Country: "Columbia", Values: Array, Date: "2015"}]


 var selectedCountries = ["Central African Republic", "Columbia"];

 var filteredCountries = countries.filter(country =>{

  ??  
 });

输出应该是包含匹配项的国家数组的过滤版本

【问题讨论】：

标签： javascript arrays

【解决方案1】：

您可以使用includes 和filter

const countries = [{GINI: 56.2, Country: "Central African Republic", Values: Array, Date: "2008"},{GINI: 51.3, Country: "Brazil", Values: Array, Date: "2015"},{GINI: 51.1, Country: "Columbia", Values: Array, Date: "2015"}]
const selectedCountries = ["Central African Republic", "Columbia"];

const filteredCountries = countries.filter(({Country})=>selectedCountries.includes(Country));

console.log(filteredCountries)

我更喜欢将selectedCountries 用作Object 而不是Array。不必每次都在 Array 上循环。

const countries = [{GINI: 56.2, Country: "Central African Republic", Values: Array, Date: "2008"},{GINI: 51.3, Country: "Brazil", Values: Array, Date: "2015"},{GINI: 51.1, Country: "Columbia", Values: Array, Date: "2015"}]

const selectedCountries = {
 "Central African Republic": true,
 "Columbia": true
};

const filteredCountries = countries.filter(({Country})=>selectedCountries[Country]);

console.log(filteredCountries)

【讨论】：

我不明白使用selectedCountries作为对象背后的想法
@ShubhDixit 比您可以直接根据键访问值。它的时间复杂度为O(1)，而在数组上为O(n)
只是为了记录，如果你能抛出一些光，它会是O(1)吗？
@ShubhDixit JS 对象使用哈希，您可以阅读此答案，这将有助于stackoverflow.com/questions/45266944/…

【解决方案2】：

使用Array.reduce() 通过Country (O(n)) 创建一个Map。然后map请求的国家列表（O（m）），并从地图中获取国家。复杂度为 O(n + m)。

const countries = [{GINI: 56.2, Country: "Central African Republic", Values: [], Date: "2008"}, {GINI: 51.3, Country: "Brazil", Values: Array, Date: "2015"},{GINI: 51.1, Country: "Columbia", Values: [], Date: "2015"}];

const selectedCountries = ["Central African Republic", "Columbia"];

const countryMap = countries.reduce((m, o) => m.set(o.Country, o), new Map);

const filteredCountries = selectedCountries.map(c => countryMap.get(c));

console.log(filteredCountries);

【讨论】：

【解决方案3】：

你可以使用array.indexOf函数

 var countries = [{GINI: 56.2, Country: "Central African Republic", Values: Array, Date: "2008"},
  {GINI: 51.3, Country: "Brazil", Values: Array, Date: "2015"},{GINI: 51.1, Country: "Columbia", Values: Array, Date: "2015"}]


 var selectedCountries = ["Central African Republic", "Columbia"];

 var filteredCountries = countries.filter(country =>selectedCountries.indexOf(country.Country)!=-1);
 console.log(filteredCountries)

【讨论】：

【解决方案4】：

您可以使用 Array.prototype.includes()

检查对象的国家/地区是否在 selectedCountries

var countries = [{
    GINI: 56.2,
    Country: "Central African Republic",
    Values: Array,
    Date: "2008"
  },
  {
    GINI: 51.3,
    Country: "Brazil",
    Values: Array,
    Date: "2015"
  }, {
    GINI: 51.1,
    Country: "Columbia",
    Values: Array,
    Date: "2015"
  }
]
var selectedCountries = ["Central African Republic", "Columbia"];
const filteredCountries = countries.filter(count => selectedCountries.includes(count.Country))
console.log(filteredCountries)

【讨论】：