Javascript : Objects with unique key within an array

Question

I have an array of objects in this form :

[
  { id:"123", url:"example1.com"},
  { id:"123", url:"example2.com"},
  { id:"456", url:"example3.com"},
  { id:"789", url:"example4.com"},
]

I'm looking for a fast performing way to filter this array to keep only objects with a unique id, in this case, the output should be :

[
  { id:"123", url:"example1.com"},
  { id:"456", url:"example3.com"},
  { id:"789", url:"example4.com"},
]

I'm using a double for loop to compare my objects, but it's painfully slow on a large array... Does anyone have a good solution?

Use the id as the index for the array instead? arr[456] = ...? Presumably id == identifier which is unique — CodingIntrigue
– CodingIntrigue, Commented Aug 19, 2014 at 11:56
Please add the code of your double for loop, just to be sure of what you're asking. — Volune
– Volune, Commented Aug 19, 2014 at 11:58
Is it not possible to do preprocessing to ensure your input isn't formatted like that in the first place? ex: Generate ids from hashing and store in a dictionary. — Rob S.
– Rob S., Commented Aug 19, 2014 at 12:02

Fender · Accepted Answer · 2014-08-19 11:59:51Z

3

See this fiddle: http://jsfiddle.net/afnvqj49/

I am using only one for loop and saving already processed keys in an object.

var a = [
  { id:"123", url:"example1.com"},
  { id:"123", url:"example2.com"},
  { id:"456", url:"example3.com"},
  { id:"789", url:"example4.com"},
];

var b = [];
var t = {};
for(var i = 0; i < a.length; i++){
    if(t[a[i].id]){
        continue;
    }
    t[a[i].id] = true;
    b.push(a[i]);
}

console.log(b);

Only the first entry for each id is kept

answered Aug 19, 2014 at 11:59

Fender

3,0551 gold badge19 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

hansmaad · Accepted Answer · 2014-08-19 12:04:38Z

2

var distinct = function(input, keyExtractor){
   var seen = {}, result = [];
   for(var i = 0, l = input.length; i < l; ++i){
      var key = keyExtractor(input[i]);
      if(seen.hasOwnProperty(key)) {
         continue;
      }
      result.push(input[i]);
      seen[key] = 1;
   }
   return result;
}

var test = [
      { id:"123", url:"example1.com"},
      { id:"123", url:"example2.com"},
      { id:"456", url:"example3.com"},
      { id:"789", url:"example4.com"},
    ];

var u = distinct(test, function(a) { return a.id; });

answered Aug 19, 2014 at 12:04

hansmaad

19k9 gold badges59 silver badges97 bronze badges

Comments

KooiInc · Accepted Answer · 2014-08-19 12:16:57Z

1

You could use Array.filter (see MDN), something like

var filtered = [
    { id:"123", url:"example1.com"},
    { id:"123", url:"example2.com"},
    { id:"456", url:"example3.com"},
    { id:"789", url:"example4.com"},
   ].filter( function (v) { 
              return !this[v.id] ? (this[v.id] = true) : false; }, 
            {});

edited Aug 19, 2014 at 12:16

answered Aug 19, 2014 at 12:09

KooiInc

124k32 gold badges145 silver badges181 bronze badges

2 Comments

0101 Over a year ago

What's the point to use ((this[v.id] = true), true) instead of just (this[v.id] = true)

KooiInc Over a year ago

None whatsoever ;). Removed it.

Samuli Hakoniemi · Accepted Answer · 2014-08-19 12:06:36Z

1

var reserved = [];
var arr = [
  { id:"123", url:"example1.com"},
  { id:"123", url:"example2.com"},
  { id:"456", url:"example3.com"},
  { id:"789", url:"example4.com"},
];

var result = arr.filter(function(item) {
  var has = ~reserved.indexOf(item.id);
  (!has && reserved.push(item.id));
  return !has;
});

answered Aug 19, 2014 at 12:06

Samuli Hakoniemi

19.1k1 gold badge64 silver badges79 bronze badges

Comments

wallop · Accepted Answer · 2014-08-19 12:03:10Z

0

window.idHolder = [];   //its better not to use window object and instead use bind.
var arr = [
  { id:"123", url:"example1.com},
  { id:"123", url:"example2.com},
  { id:"456", url:"example3.com},
  { id:"789", url:"example4.com},
];

var uniqueArr = arr.filter(function(val)
{
if(window.idHolder.indexOf(val.id)!=-1)
{
return false;
}
else
{
window.idHolder.push(val.id);
return true;
}

});

Unique arr will have what you asked for

answered Aug 19, 2014 at 12:03

wallop

2,6011 gold badge29 silver badges39 bronze badges

Comments

ffflabs · Accepted Answer · 2014-08-19 12:08:00Z

0

Since there are plenty of good answers, I just want to throw mine in for fun.

A one-liner using underscore's groupBy and map methods.

_.map(_.groupBy(yourarray,function(element) { return element.id }),function(element) { return element[0] });

PD: is it customary to upvote several answers when they are all correct? perhaps I've been breaking SO Etiquette unknowingly.

answered Aug 19, 2014 at 12:08

ffflabs

17.6k5 gold badges57 silver badges79 bronze badges

1 Comment

Paolo Moretti Over a year ago

_.uniq is better: _.uniq(urls, function(url) { return url.id }); :-)

Collectives™ on Stack Overflow

Javascript : Objects with unique key within an array

6 Answers 6

Comments

Comments

2 Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

2 Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related