Delete duplicate elements from Array in Javascript

Question

I have array with obejcts email and Id so I want delete duplicate elements who have similar ID's.

Example:

var newarray=[
    {
        Email:"test1@gmail.com",
        ID:"A"
    },
    {
        Email:"test2@gmail.com",
        ID:"B"
    },
    {
        Email:"test3@gmail.com",
        ID:"A"
    },
    {
        Email:"test4@gmail.com",
        ID:"C"
    },
    {
        Email:"test4@gmail.com",
        ID:"C"
    }
];

Now I need to delete Duplicate elements which have ID's are common.In the sence I am expecting final Array is

var FinalArray=[
    {
        Email:"test1@gmail.com",
        ID:"A"
    },
    {
        Email:"test2@gmail.com",
        ID:"B"
    },  
    {
        Email:"test5@gmail.com",
        ID:"C"
    }
];

All you need is to simply create a new array, iterate through your original array and fill new array with those items which are not duplicate. Of course, you may want to improve this performance by using object or Map or whatever else, but idea is the same. — Yeldar Kurmangaliyev, Nov 08 '16 at 08:52
You expect `test1` for `ID:"A"` but `test5` for `ID:"C"`. Does it mean you don't care which duplicate is filtered out? — pawel, Nov 08 '16 at 08:54
Why marked as duplicate???? Can any one find any codes from the linked question that solve this question?? — tsh, Mar 02 '18 at 04:14
Here is one good way to achieve this: https://stackoverflow.com/questions/15125920/how-to-get-distinct-values-from-an-array-of-objects-in-javascript/58429784#58429784 — Arun Saini, Jul 24 '20 at 18:28

score 6 · Accepted Answer · answered Nov 08 '16 at 08:52

Use Array.prototype.filter to filter out the elements and to keep a check of duplicates use a temp array

var newarray = [{
  Email: "test1@gmail.com",
  ID: "A"
}, {
  Email: "test2@gmail.com",
  ID: "B"
}, {
  Email: "test3@gmail.com",
  ID: "A"
}, {
  Email: "test4@gmail.com",
  ID: "C"
}, {
  Email: "test5@gmail.com",
  ID: "C"
}];
   
// Array to keep track of duplicates
var dups = [];
var arr = newarray.filter(function(el) {
  // If it is not a duplicate, return true
  if (dups.indexOf(el.ID) == -1) {
    dups.push(el.ID);
    return true;
  }

  return false;
  
});

console.log(arr);

Nina Scholz · Answer 2 · 2016-11-08T09:05:40.037

You could filter it with a hash table.

var newarray = [{ Email: "test1@gmail.com", ID: "A" }, { Email: "test2@gmail.com", ID: "B" }, { Email: "test3@gmail.com", ID: "A" }, { Email: "test4@gmail.com", ID: "C" }, { Email: "test5@gmail.com", ID: "C" }],
    filtered = newarray.filter(function (a) {
        if (!this[a.ID]) {
            this[a.ID] = true;
            return true;
        }
    }, Object.create(null));

console.log(filtered);

.as-console-wrapper { max-height: 100% !important; top: 0; }

ES6 with Set

var newarray = [{ Email: "test1@gmail.com", ID: "A" }, { Email: "test2@gmail.com", ID: "B" }, { Email: "test3@gmail.com", ID: "A" }, { Email: "test4@gmail.com", ID: "C" }, { Email: "test5@gmail.com", ID: "C" }],
    filtered = newarray.filter((s => a => !s.has(a.ID) && s.add(a.ID))(new Set));

console.log(filtered);

.as-console-wrapper { max-height: 100% !important; top: 0; }

score 2 · Answer 3 · answered Nov 08 '16 at 08:52

If you can use Javascript libraries such as underscore or lodash, I recommend having a look at _.uniq function in their libraries. From lodash:

_.uniq(array, [isSorted=false], [callback=_.identity], [thisArg])

Here you have to use like below,

var non_duplidated_data = _.uniq(newarray, 'ID');

score 1 · Answer 4 · answered Nov 08 '16 at 09:00

Another solution using Array.prototype.reduce and a hash table - see demo below:

var newarray=[ { Email:"test1@gmail.com", ID:"A" }, { Email:"test2@gmail.com", ID:"B" }, { Email:"test3@gmail.com", ID:"A" }, { Email:"test4@gmail.com", ID:"C" }, { Email:"test5@gmail.com", ID:"C" } ];

var result = newarray.reduce(function(hash){
  return function(prev,curr){
     !hash[curr.ID] && (hash[curr.ID]=prev.push(curr));
     return prev;
  };
}(Object.create(null)),[]);

console.log(result);

.as-console-wrapper{top:0;max-height:100%!important;}

@SantoshKhavekar let me know (and vote up too!) if this answer helped you, thanks! — kukkuz, Nov 08 '16 at 10:38

Delete duplicate elements from Array in Javascript

4 Answers4

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