Using underscore unique on object

Question

I would like to return a unique array where the room object is the same.

var input = [
  {
    position:{
      room: {
        name: 'WC',
        number: '001'
      }
    }
  },
  {
    position:{
      room: {
        name: 'WC',
        number: '001'
      }
    }
  },
  {
    position:{
      room: {
        name: 'RWC',
        number: '007'
      }
    }
  }
];

So this list would be:

var input = [
  {
    position:{
      room: {
        name: 'WC',
        number: '001'
      }
    }
  },
  {
    position:{
      room: {
        name: 'RWC',
        number: '007'
      }
    }
  }
];

I tried this:

  var distinctRooms = _.uniq(input, function(input){
    return input.position.room
  });

But it returns the entire list. Have not seen any example where you compare objects. Is this possible to do somehow with the _uniq?

score 1 · Answer 1 · answered Aug 19 '14 at 14:39

1

Room objects are different. If you consider rooms to be equal based on their numbers you can use

  var distinctRooms = _.uniq(input, function(input){
    return input.position.room.number;
  });

answered Aug 19 '14 at 14:39

Yury Tarabanko

44,270
9
84
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1

that would discard rooms with matching numbers, even if names were different, which isn't what OP is asking – ffflabs Aug 19 '14 at 14:42
@amenadiel How do you know OP has rooms with the same numbers but different names? :) Sounds like a nonusual case to me. – Yury Tarabanko Aug 19 '14 at 14:45
it's a gift I've had since childhood ;) – ffflabs Aug 19 '14 at 14:55

score 0 · Answer 2 · edited May 23 '17 at 11:57

0

Maybe you should take a look at this answer where he iterates and creates an array with unique values.

edited May 23 '17 at 11:57

Community

1
1

answered Aug 19 '14 at 14:42

rafaelune

59
6

score 0 · Answer 3 · edited May 23 '17 at 11:57

Using the _.isEqual() function that provides deep object comparison it is possible to create a function that applies it to an array of objects and create a mix-in from that function.

Algorithm:

take the first element from the list (the head), store it in the result
iterate the rest of the list (the tail), remove every element that .isEqual to the first element
if the rest of the list is not empty, pass it to step 1, otherwise return the result

Code, implemented with a recursive approach:

_.mixin({
    deepUniq: (function () {
        var dedup = function (coll, result) {
            var head = _.first(coll),
                tail = _.reject(_.rest(coll), function (curr) {
                    return _.isEqual(curr, head);
                });

            result.push(head);
            return (tail.length) ? dedup(tail, result) : result;
        };
        return function (coll) {
            return dedup(coll, []);
        };
    })()
});

A word of warning: This approach has exponential running time, i.e. it will be increasingly slow for long lists of deeply nested objects. My advice would be to compare correctness and performance of different solutions.

Disclaimer: This solution is based on https://stackoverflow.com/a/19641747/

score -1 · Accepted Answer · answered Aug 19 '14 at 14:38

-1

As long as you don't have circular structures, you can use JSON Stringify to make a deep comparison of every room attribute

_.uniq(input, function(input){
    return JSON.stringify(input.position.room)
  });

answered Aug 19 '14 at 14:38

ffflabs

17,166
5
51
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2

Properties of non-array objects are not guaranteed to be stringified in any particular order. – Yury Tarabanko Aug 19 '14 at 14:40
You're right. I guess you could extract the object keys and use _.sort to provide a sorted copy. It seems like a lot of overkill :( – ffflabs Aug 19 '14 at 14:43
Isn't there a badge for a -1 rated accepted answer? ¬¬ – ffflabs Aug 19 '14 at 14:53
1

There should be one for creating a Heisenbug. :) – Yury Tarabanko Aug 19 '14 at 14:56
@amenadiel, haha, I don't really what you are talking about but your code works as expected. – Joe Aug 19 '14 at 14:57
@YuryTarabanko whoa I there's a concept I hadn't heard of! – ffflabs Aug 19 '14 at 14:57
2

@user1572526 Beware that you are relying on undefined behaviour. :) `var isAlive = JSON.stringify({name: 1, number: 2}) === JSON.stringify({number: 2, name: 1})` - is pure quantum mechanics. :) – Yury Tarabanko Aug 19 '14 at 15:00
A reasonable bet would be to `return input.position.room.name + input.position.room.number` – PSL Aug 19 '14 at 15:07

Using underscore unique on object

4 Answers4