Remove duplicate objects from an array using javascript

Question

I am trying to figure out an efficient way to remove objects that are duplicates from an array and looking for the most efficient answer. I looked around the internet everyt

Answer 1

I see, the problem there is that the complexity is squared. There is one trick to do it, it's simply by using "Associative arrays".

You can get the array, loop over it, and add the value of the array as a key to the associative array. Since it doesn't allow duplicated keys, you will automatically get rid of the duplicates.

Since you are looking for title and artist when comparing, you can actually try to use something like:

var arrResult = {};
for (i = 0, n = arr.length; i < n; i++) {
    var item = arr[i];
    arrResult[ item.title + " - " + item.artist ] = item;
}

Then you just loop the arrResult again, and recreate the array.

var i = 0;
var nonDuplicatedArray = [];    
for(var item in arrResult) {
    nonDuplicatedArray[i++] = arrResult[item];
}

Updated to include Paul's comment. Thanks!

Answer 2

If you are using underscore js, it is easy to remove duplicate object. http://underscorejs.org/#uniq

Answer 3

Basic sort-then-unique implementation, fiddle HERE:

function unique(arr) {
    var comparer = function compareObject(a, b) {
        if (a.title == b.title) {
            if (a.artist < b.artist) {
                return -1;
            } else if (a.artist > b.artist) {
                return 1;
            } else {
                return 0;
            }
        } else {
            if (a.title < b.title) {
                return -1;
            } else {
                return 1;
            }
        }
    }

    arr.sort(comparer);
    console.log("Sorted: " + JSON.stringify(arr));
    for (var i = 0; i < arr.length - 1; ++i) {
        if (comparer(arr[i], arr[i+1]) === 0) {
            arr.splice(i, 1);
            console.log("Splicing: " + JSON.stringify(arr));
        }
    }
    return arr;
}

It may or may not be the most efficient, and should be entirely scalable. I've added some console.logs so you can see it as it works.

EDIT

In the interest of saving on the space the function used, I did that for loop at the end, but it seems likely that didn't properly find only unique results (depsite it passing my simple jsfiddle test). Please try replacing my for loop with the following:

var checker;
var uniqueResults = [];
for (var i = 0; i < arr.length; ++i) {
    if (!checker || comparer(checker, arr[i]) != 0) {
        checker = arr[i];
        uniqueResults.push(checker);
    }
}
return uniqueResults;

Answer 4

Below code compares object with JSON as String format and removes duplicates and works fine with simple arrays.

    Array.prototype.unique=function(a){
     return function(){
        return this.filter(a)
     }
   }(
   function(a,b,c){
     var tmp=[]; 
     c.forEach(function(el){
        tmp.push(JSON.stringify(el))
    }); 
    return tmp.indexOf(JSON.stringify(a),b+1)<0
  })

Answer 5

function remove_duplicates(objectsArray) {
    var arr = [], collection = []; 
    $.each(objectsArray, function (index, value) {
        if ($.inArray(value.id, arr) == -1) { 
            arr.push(value.id);
            collection.push(value);
        }
    });
    return collection;
}

Answer 6

For those who love ES6 and short stuff, here it's one solution:

const arr = [
  { title: "sky", artist: "Jon" },
  { title: "rain", artist: "Paul" },
  { title: "sky", artist: "Jon" }
];

Array.from(arr.reduce((a, o) => a.set(o.title, o), new Map()).values());

const arr = [
  { title: "sky", artist: "Jon" },
  { title: "rain", artist: "Paul" },
  { title: "sky", artist: "Jon" },
  { title: "rain", artist: "Jon" },
  { title: "cry", artist: "Jon" }
];

const unique = Array.from(arr.reduce((a, o) => a.set(o.title, o), new Map()).values());

console.log(`New array length: ${unique.length}`)

console.log(unique)

The above example only works for a unique title or id. Basically, it creates a new map for songs with duplicate titles.