Filtering duplicate hashes from array of hashes - Javascript

Question

I have an array of hashes, like this:

[{id: "4bf58dd8d48988d110941735", name: "italy"},
 {id: "4bf58dd8d48988d1c6941735", name: "skandi"},
 {id: "4bf58dd8d48988d147941735", name: "diner"},
 {id: "4bf58dd8d48988d110941735", name: "italy"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"},
 {id: "4bf58dd8d48988d14a941735", name: "vietnam"},
 {id: "4bf58dd8d48988d1ce941735", name: "fish"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"}]

I want to throw out duplicate hashes. Set doesn't work because hashes are unique objects.

I feel stuck and need a kick to think. Please advise!

Reduce the array to an object, using the id as key, and then convert back to array using Object.values(). — Ori Drori
– Ori Drori, Commented Dec 21, 2018 at 9:44
You would have to loop through the array for each possible hash and check, remove. Or change the data format, use an object with the hash string as a key and the name and whatever else as a separate object for the value — Patrick Evans
– Patrick Evans, Commented Dec 21, 2018 at 9:46

Just code · Accepted Answer · 2018-12-21 11:50:08Z

7

You can use reduce too

//I added comma to each object
const data= [{id: "4bf58dd8d48988d110941735", name: "italy"},
    {id: "4bf58dd8d48988d1c6941735", name: "skandi"},
    {id: "4bf58dd8d48988d147941735", name: "diner"},
    {id: "4bf58dd8d48988d110941735", name: "italy"},
    {id: "4bf58dd8d48988d1c4941735", name: "resto"},
    {id: "4bf58dd8d48988d14a941735", name: "vietnam"},
    {id: "4bf58dd8d48988d1ce941735", name: "fish"},
    {id: "4bf58dd8d48988d1c4941735", name: "resto"},
    {id: "4bf58dd8d48988d1c4941735", name: "resto"}]

const result= data.reduce((current,next)=>{   
    if(!current.some(a=> a.name === next.name)){
        current.push(next);
    }
    return current;
},[])
console.log(result);

edited Dec 21, 2018 at 11:50

answered Dec 21, 2018 at 10:04

Just code

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Comments

Kamil Kiełczewski · Accepted Answer · 2019-01-14 03:41:34Z

6

Try this

h.filter(( t={}, a=>!(t[a.id]=a.id in t) ))

Input array in h, time complexity O(n), explanation here .

let h = [{id: "4bf58dd8d48988d110941735", name: "italy"},
 {id: "4bf58dd8d48988d1c6941735", name: "skandi"},
 {id: "4bf58dd8d48988d147941735", name: "diner"},
 {id: "4bf58dd8d48988d110941735", name: "italy"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"},
 {id: "4bf58dd8d48988d14a941735", name: "vietnam"},
 {id: "4bf58dd8d48988d1ce941735", name: "fish"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"},
 {id: "4bf58dd8d48988d1c4941735", name: "resto"}]
 
 let t; // declare t to avoid use global (however works without it too)
 let r= h.filter(( t={}, a=>!(t[a.id]=a.id in t) ))

 
 console.log(JSON.stringify(r));

edited Jan 14, 2019 at 3:41

answered Dec 21, 2018 at 9:45

Kamil Kiełczewski

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Comments

zheng li · Accepted Answer · 2018-12-21 10:03:51Z

4

Space for time

let arr = [
    { id: '4bf58dd8d48988d110941735', name: 'italy' },
    { id: '4bf58dd8d48988d1c6941735', name: 'skandi' },
    { id: '4bf58dd8d48988d147941735', name: 'diner' },
    { id: '4bf58dd8d48988d110941735', name: 'italy' },
    { id: '4bf58dd8d48988d1c4941735', name: 'resto' },
    { id: '4bf58dd8d48988d14a941735', name: 'vietnam' },
    { id: '4bf58dd8d48988d1ce941735', name: 'fish' },
    { id: '4bf58dd8d48988d1c4941735', name: 'resto' },
    { id: '4bf58dd8d48988d1c4941735', name: 'resto' }
]

let map = {};
let rest = arr.filter((item) => {
    if(map[item.id] === void 0) {
        map[item.id] = item.id;
        return true;
    }
});
map = null;

console.log(rest);

answered Dec 21, 2018 at 10:03

zheng li

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Comments

Stephan T. · Accepted Answer · 2018-12-21 10:00:03Z

2

I would suggest an approach with associative arrays, this makes duplicate removal easier. If you can, you should build your array as an associative array in the first place, so that you don't have to convert it. Here is how you do it:

var array = [{
    id: "4bf58dd8d48988d110941735",
    name: "italy"
  },
  {
    id: "4bf58dd8d48988d1c6941735",
    name: "skandi"
  }, {
    id: "4bf58dd8d48988d147941735",
    name: "diner"
  }, {
    id: "4bf58dd8d48988d110941735",
    name: "italy"
  }, {
    id: "4bf58dd8d48988d1c4941735",
    name: "resto"
  }, {
    id: "4bf58dd8d48988d14a941735",
    name: "vietnam"
  }, {
    id: "4bf58dd8d48988d14a941735",
    name: "fish"
  }, {
    id: "4bf58dd8d48988d1c4941735",
    name: "resto"
  }, {
    id: "4bf58dd8d48988d1c4941735",
    name: "resto"
  }
];

// you can access the array with arrayAssociative[id], where the id is the real id like "4bf58dd8d48988d110941735"
var arrayAssociative = {};
for (item in array) {
  // first get the unique id's
  var addedNode = arrayAssociative[array[item].id] = arrayAssociative[array[item].id] || {};
  if (addedNode.names == null)
    addedNode.names = {};
  // now get the unique names
  var addedName = arrayAssociative[array[item].id].names[array[item].name] = arrayAssociative[array[item].id].names[array[item].name] || {};
}
console.log(arrayAssociative);

I don't know the exact reason, why the line

var element = arrayAssociative[id] =arrayAssociative[id] || {};

works for this, but let's just accept the funcitonality as it is :)

edited Dec 21, 2018 at 10:00

answered Dec 21, 2018 at 9:52

Stephan T.

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1 Comment

Kamil Kiełczewski Over a year ago

arrayAssociative[array[item].id] || {} this line gives value in left of || if it is not null/undefined/0/false or value in the right if opposit - stackoverflow.com/q/2100758/860099

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