[javascript] Removing duplicate objects with Underscore for Javascript

I have this kind of array:

var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];

I'd like to filter it to have:

var bar = [ { "a" : "1" }, { "b" : "2" }];

I tried using _.uniq, but I guess because { "a" : "1" } is not equal to itself, it doesn't work. Is there any way to provide underscore uniq with an overriden equals function?

The lodash 4.6.1 docs have this as an example for object key equality:

_.uniqWith(objects, _.isEqual);

https://lodash.com/docs#uniqWith

.uniq/.unique accepts a callback

var list = [{a:1,b:5},{a:1,c:5},{a:2},{a:3},{a:4},{a:3},{a:2}];

var uniqueList = _.uniq(list, function(item, key, a) { 
    return item.a;
});

// uniqueList = [Object {a=1, b=5}, Object {a=2}, Object {a=3}, Object {a=4}]

Notes:

1. Callback return value used for comparison
2. First comparison object with unique return value used as unique
3. underscorejs.org demonstrates no callback usage
4. lodash.com shows usage

Another example : using the callback to extract car makes, colors from a list

I wanted to solve this simple solution in a straightforward way of writing, with a little bit of a pain of computational expenses... but isn't it a trivial solution with a minimum variable definition, is it?

function uniq(ArrayObjects){
  var out = []
  ArrayObjects.map(obj => {
    if(_.every(out, outobj => !_.isEqual(obj, outobj))) out.push(obj)
  })
  return out
}

When I have an attribute id, this is my preffered way in underscore:

var x = [{i:2}, {i:2, x:42}, {i:4}, {i:3}];
_.chain(x).indexBy("i").values().value();
// > [{i:2, x:42}, {i:4}, {i:3}]

here's my solution (coffeescript) :

_.mixin
  deepUniq: (coll) ->
    result = []
    remove_first_el_duplicates = (coll2) ->

      rest = _.rest(coll2)
      first = _.first(coll2)
      result.push first
      equalsFirst = (el) -> _.isEqual(el,first)

      newColl = _.reject rest, equalsFirst

      unless _.isEmpty newColl
        remove_first_el_duplicates newColl

    remove_first_el_duplicates(coll)
    result

example:

_.deepUniq([ {a:1,b:12}, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ],[ 2, 1, 2, 1 ], {a:1,b:12} ]) 
//=> [ { a: 1, b: 12 }, [ 2, 1, 2, 1 ], [ 1, 2, 1, 2 ] ]

If you're looking to remove duplicates based on an id you could do something like this:

var res = [
  {id: 1, content: 'heeey'},
  {id: 2, content: 'woah'}, 
  {id: 1, content:'foo'},
  {id: 1, content: 'heeey'},
];
var uniques = _.map(_.groupBy(res,function(doc){
  return doc.id;
}),function(grouped){
  return grouped[0];
});

//uniques
//[{id: 1, content: 'heeey'},{id: 2, content: 'woah'}]

Try iterator function

For example you can return first element

x = [['a',1],['b',2],['a',1]]

_.uniq(x,false,function(i){  

   return i[0]   //'a','b'

})

=> [['a',1],['b',2]]

Here is a simple solution, which uses a deep object comparison to check for duplicates (without resorting to converting to JSON, which is inefficient and hacky)

var newArr = _.filter(oldArr, function (element, index) {
    // tests if the element has a duplicate in the rest of the array
    for(index += 1; index < oldArr.length; index += 1) {
        if (_.isEqual(element, oldArr[index])) {
            return false;
        }
    }
    return true;
});

It filters out all elements if they have a duplicate later in the array - such that the last duplicate element is kept.

The testing for a duplicate uses _.isEqual which performs an optimised deep comparison between the two objects see the underscore isEqual documentation for more info.

edit: updated to use _.filter which is a cleaner approach

You can do it in a shorthand as:

_.uniq(foo, 'a')

with underscore i had to use String() in the iteratee function

function isUniq(item) {
    return String(item.user);
}
var myUniqArray = _.uniq(myArray, isUniq);

Implementation of Shiplu's answer.

var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];

var x = _.uniq( _.collect( foo, function( x ){
    return JSON.stringify( x );
}));

console.log( x ); // returns [ { "a" : "1" }, { "b" : "2" } ]

var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
var bar = _.map(_.groupBy(foo, function (f) { 
        return JSON.stringify(f); 
    }), function (gr) { 
        return gr[0]; 
    }
);

Lets break this down. First lets group the array items by their stringified value

var grouped = _.groupBy(foo, function (f) { 
    return JSON.stringify(f); 
});

grouped looks like:

{
    '{ "a" : "1" }' = [ { "a" : "1" } { "a" : "1" } ],
    '{ "b" : "2" }' = [ { "b" : "2" } ]
}

Then lets grab the first element from each group

var bar = _.map(grouped, function(gr)
    return gr[0]; 
});

bar looks like: [ { "a" : "1" }, { "b" : "2" } ]

Put it all together:

var foo = [ { "a" : "1" }, { "b" : "2" }, { "a" : "1" } ];
var bar = _.map(_.groupBy(foo, function (f) { 
        return JSON.stringify(f); 
    }), function (gr) { 
        return gr[0]; 
    }
);

Using underscore unique lib following is working for me, I m making list unique on the based of _id then returning String value of _id:

var uniqueEntities = _.uniq(entities, function (item, key, a) {
                                    return item._id.toString();
                                });