How do I remove duplicate objects in an array by field in Javascript?

Question

I have an array of objects:

[{
  id: 1,
  name: 'kitten'
}, {
  id: 2,
  name: 'kitten'
},{
  id: 3,
  name: 'cat
}]

How do I remove the second kitten? Sorting into an array of names doesn't work, because I can't know if I am deleting id 1 or or id 2. So, I'm not quite sure how to do this.

Do you get the array from somewhere or you create it yourself? Because if you create it yourself it would be wise to check for duplicates before insertion. — cezar, Jun 16 '15 at 11:07
http://stackoverflow.com/questions/9229645/remove-duplicates-from-javascript-array — Warren Grimskin, Jun 16 '15 at 11:08

Ivan Mushketyk · Answer 1 · 2015-06-16T11:41:09.087

1

You can use an additional hash-map to store names found so far. When you process a next object if it's name is already in the hash-map it is a duplicate and you can remove it.

var duplicates = {};
for (var i = 0; i < array.length) {
    var obj = array[i];

    if (! duplicates[obj.name]) {
        duplicates[obj.name] = 1;
        i++;
    } else {
        array.splice(i, 1);
    }
}

edited Jun 16 '15 at 11:41

answered Jun 16 '15 at 11:07

Ivan Mushketyk

8,107
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Do you have an example piece of code I could look at, for that? I know that this is possible in other languages, I just haven't encountered hash maps before in JS. – RichLitt Jun 16 '15 at 11:13

score 0 · Accepted Answer · answered Jun 16 '15 at 11:16

0

there is the lodash library. You could use the uniq

var array = [{
  id: 1,
  name: 'kitten'
}, {
  id: 2,
  name: 'kitten'
},{
  id: 3,
  name: 'cat'
}];


var asd = _.uniq(array,'name');

console.log(asd);

Gives an output:

[ { id: 1, name: 'kitten' }, { id: 3, name: 'cat' } ]

as it written in the documentation "only the first occurence of each element is kept".

answered Jun 16 '15 at 11:16

cs04iz1

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Yeah, I thought of that too. The issue is that I need to find the ID of the excluded item in order to delete it through an API. Not sure how to get that. Perhaps a set function that shows me the difference? – RichLitt Jun 16 '15 at 11:19
1

yes you could do that. use the difference function of lodash, doing the following var asd = _.uniq(array,'name'); console.log(asd); var dif = _.difference(array,asd); console.log(dif); – cs04iz1 Jun 16 '15 at 11:35

score 0 · Answer 3 · answered Jun 16 '15 at 11:22

    var arr =[{
      id: 1,
      name: 'kitten'
    }, {
      id: 2,
      name: 'kitten'
    },{
      id: 3,
      name: 'cat'
    }];
    var results = [];
    var idsSeen = {}, idSeenValue = {};
    for (var i = 0, len = arr.length, name; i < len; ++i) {
        name = arr[i].name;
        if (idsSeen[name] !== idSeenValue) {
            results.push(arr[i]);
            idsSeen[name] = idSeenValue;
        }
    }
    console.log(results);

How do I remove duplicate objects in an array by field in Javascript?

3 Answers3