Best way to filter the array of objects

Question

I have an array of objects with a property I want to filter on called "Country". I have the user select which countries they want to see and wish to return an array of objects filtered by that property. What is the most efficient way to complete this process?

  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 =>{

  ??  
 });

Output should be a filtered version of the countries array containing the matches

Code Maniac · Accepted Answer · 2019-02-09T16:51:24.053

2

You can use includes and 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)

I will prefer to have selectedCountries as an Object instead of an Array. Than need not to loop on Array every time.

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)

edited Feb 09 '19 at 16:51

answered Feb 09 '19 at 16:40

Code Maniac

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I din't understand the idea behind using `selectedCountries` as object – Shubham Dixit Feb 09 '19 at 16:55
@ShubhDixit than you can directly access value based on key. it will have time complexity of `O(1)` while on array it will be `O(n)` – Code Maniac Feb 09 '19 at 16:56
Just for the record ,how will it be O(1) ,if you can throw some light? – Shubham Dixit Feb 09 '19 at 16:58
1

@ShubhDixit JS objects uses hashes you can read this answer this will help https://stackoverflow.com/questions/45266944/complexity-of-accessing-data-in-an-object – Code Maniac Feb 09 '19 at 17:01

score 0 · Answer 2 · edited Feb 09 '19 at 16:48

You can use check if the Country of the object is in selectedCountries using Array.prototype.includes()

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)

score 0 · Answer 3 · answered Feb 09 '19 at 16:43

Create a Map by Country (O(n)) using Array.reduce(). Then map the list of requested countries (O(m)), and get the country from the Map. The complexity would be 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);

score 0 · Answer 4 · answered Feb 09 '19 at 16:44

You can use of array.indexOf function

 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)

Best way to filter the array of objects

4 Answers4