Now I have two object arrays,

var arr1 = [{id: 0, name: 'Jack'}, {id: 1, name: 'Ben'}, {id: 2, name: 'Leon'}, {id: 3, name: 'Gavin'}];
var arr2 =  [{id: 0, name: 'Jack'}, {id: 5, name: 'Jet'}, {id: 2, name: 'Leon'}];

I want to remove those objects of same id in arr1 and arr2, so the results are:

var arr1 = [{id: 1, name: 'Ben'}, {id: 3, name: 'Gavin'}];
var arr2 =  [{id: 5, name: 'Jet'}];

How to implement it with lodash or underscore?

Here are my implementation.

arr1_ids = _.pluck(arr1, 'id');
arr2_ids = _.pluck(arr2, 'id');

same_ids = _.intersection(arr1_ids, arr2_ids);

arr1 = _.remove(arr1, function(e) { return !_.contains(same_ids, e.id); });
arr2 = _.remove(arr2, function(e) { return !_.contains(same_ids, e.id); });

Is there any better way to do that?

Now I have two object arrays,

var arr1 = [{id: 0, name: 'Jack'}, {id: 1, name: 'Ben'}, {id: 2, name: 'Leon'}, {id: 3, name: 'Gavin'}];
var arr2 =  [{id: 0, name: 'Jack'}, {id: 5, name: 'Jet'}, {id: 2, name: 'Leon'}];

I want to remove those objects of same id in arr1 and arr2, so the results are:

var arr1 = [{id: 1, name: 'Ben'}, {id: 3, name: 'Gavin'}];
var arr2 =  [{id: 5, name: 'Jet'}];

How to implement it with lodash or underscore?

Here are my implementation.

arr1_ids = _.pluck(arr1, 'id');
arr2_ids = _.pluck(arr2, 'id');

same_ids = _.intersection(arr1_ids, arr2_ids);

arr1 = _.remove(arr1, function(e) { return !_.contains(same_ids, e.id); });
arr2 = _.remove(arr2, function(e) { return !_.contains(same_ids, e.id); });

Is there any better way to do that?

• javascript
• arrays
• underscore.js
• lodash

• Cant this be acplished with .uniq? – Dom Commented May 27, 2015 at 4:15
• How to do that with uniq? – zangw Commented May 27, 2015 at 4:28
• Define "better". Is that faster? Less code? Easier to maintain? ;-) – RobG Commented May 29, 2015 at 21:56

3 Answers 3

Can you use _.difference?

same_elements = _.intersection(arr1, arr2);
arr1 = _.difference(arr1, same_elements);
arr2 = _.difference(arr2, same_elements);

I'm not sure how this should be done with underscore or lodash, but here's a JavaScript implementation.

It creates a filter function that you can then apply to both arrays to only keep the elements that aren't part of the intersection.

var arr1 = [{id: 0, name: 'Jack'}, {id: 1, name: 'Ben'}, {id: 2, name: 'Leon'}, {id: 3, name: 'Gavin'}];
var arr2 =  [{id: 0, name: 'Jack'}, {id: 5, name: 'Jet'}, {id: 2, name: 'Leon'}];

var negative_intersection_filter = function(a, b) {
  // create a map to speed up the filtering later
  var map = a.reduce(function(map, current) {
    // perform the intersection
    map[current.id] = b.some(function(item) {
      return item.id == current.id;
    });
    return map;
  }, {});

  // our filtering function, simple
  return function(item) {
    return !map[item.id];
  }
}(arr1, arr2);

// apply the filter here
arr1 = arr1.filter(negative_intersection_filter);
arr2 = arr2.filter(negative_intersection_filter);
console.log(arr1);
console.log(arr2);

I think your algorithm is about right, here's a slightly different approach in plain js. I've used a, b instead of arr1, arr2 for brevity:

// Collect ids and sort
var ids = a.map(function(obj) {return obj.id}).concat(b.map(function(obj) {return obj.id})).sort();

// Get IDs that aren't duplicates
var nonDups = ids.filter(function(v, i, o){return v !== o[i-1] && v !== o[i+1]});

// Keep only the non-duplicates in each array
a.reduceRight(function(pre, cur, i, o){if (nonDups.indexOf(cur.id) == -1) o.splice(i, 1)},0);
b.reduceRight(function(pre, cur, i, o){if (nonDups.indexOf(cur.id) == -1) o.splice(i, 1)},0);

JSON.stringify(a)  // [{"id":1,"name":"Ben"},{"id":3,"name":"Gavin"}]
JSON.stringify(b)  // [{"id":5,"name":"Jet"}]

reduceRight is just used to iterate over each array backwards so that splicing doesn't affect the iteration.