Comparing two arrays which contain objects

Question

I have two arrays which only contain objects for groups. One contains all the groups on my site. The other contains all the groups a specific user belongs to.

I'd like to subtract: All the groups - user groups = groups remaining

I'm using AngularJS, I'm not sure if that helps here or not (maybe a filter could be used).

I looked at previous questions and came across some options:

These are the ones I tried:

$scope.availableGroups =  $($scope.groups).not($scope.assignedGroups).get();
$scope.availableGroups = $.grep($scope.groups,function(x) {return $.inArray(x, $scope.assignedGroups) < 0})

This is one of the arrays:

assignedGroups:

[{
    id: 115,
    name: 'Test Group 2',
    Description: '',
    owner: 10,
    OwnerIsUser: false,
}, {
    id: 116,
    name: 'Test Group 3',
    Description: '',
    owner: 71,
    OwnerIsUser: false,
}, {
    id: 117,
    name: 'Test Group 4',
    Description: '',
    owner: 71,
    OwnerIsUser: false,
}, {
    id: 118,
    name: 'Test Group 5',
    Description: '',
    owner: 115,
    OwnerIsUser: false,
}, {
    id: 119,
    name: 'Test Group 6',
    Description: '',
    owner: 8,
    OwnerIsUser: true,
}];

Answer 1

I think you should extract ids to an object first and then compare two objects. Eg:

var assignedGroupsIds = {};
var groupsIds = {};
var result = [];

$scope.assignedGroups.forEach(function (el, i) {
  assignedGroupsIds[el.id] = $scope.assignedGroups[i];
});

$scope.groups.forEach(function (el, i) {
  groupsIds[el.id] = $scope.groups[i];
});

for (var i in groupsIds) {
    if (!assignedGroupsIds.hasOwnProperty(i)) {
        result.push(groupsIds[i]);
    }
}

return result;

Here goes simplified fiddle: http://jsfiddle.net/NLQGL/2/ Adjust it to your needs.

I think it's a good solution since you could reuse the groupsIds object (it seems not to change often).

Note: Feel free to use angular.forEach() instead of Array.prototype.forEach

Answer 2

You can use a combination of Angular JS's $filter service and Lo-dash's findWhere method to get unique objects in two arrays, try this :

// When you don't know the lengths of the arrays you want to compare
    var allTheGroupsLength = allTheGroups.length;
    var userGroupsLength = userGroups.length;
    var groupsRemaining = [];

    if(allTheGroupsLength > userGroupsLength){
        getDifference(allTheGroups, userGroups);
    }
    else{
        getDifference(userGroups, allTheGroups);
    }

    function getDifference(obj1, obj2){
        groupsRemaining  = $filter('filter')(obj1, function(obj1Value){
              return !Boolean(_.findWhere(obj2, obj1Value));
        });
    }

OR

//All the groups - user groups = groups remaining

 groupsRemaining  = $filter('filter')(allTheGroups, function(allTheGroupsObj){
                  return !Boolean(_.findWhere(userGroups, allTheGroupsObj));
              });

Using only Angular JS

  groupsRemaining =  $filter('filter')(allTheGroups, function(allTheGroupsObj){
                      return !angular.equals(allTheGroupsObj, $filter('filter')(userGroups, function(userGroupsObj){
                      return angular.equals(allTheGroupsObj,userGroupsObj);})[0]);
                  });

Answer 3

You can try this

// .compare method to Array's prototype to call it on any array
Array.prototype.compare = function (array) 
{
    if (!array)
        return false;

    // compare lengths
    if (this.length != array.length)
        return false;

    for (var i = 0, l = this.length; i < l; i++)
    {
        if (this[i] instanceof Array && array[i] instanceof Array) 
        {
           if (!this[i].compare(array[i]))
              return false;
        }
        else if (this[i] != array[i])
        {
            return false;
        }
    }
    return true;
}

Result

[1, 2, [3, 4]].compare([1, 2, [3, 4]]) === true;
[1, 2, 1, 2].compare([1, 2, 1, 2]) === true;

Json Diff

function diff(obj1, obj2)
 {
    var result = {};
    $.each(obj1, function (key, value)
    {
        if (!obj2.hasOwnProperty(key) || obj2[key] !== obj1[key])
        {
            result[key] = value;
        }
    });

    return result;
}

Answer 4

(maybe a filter could be used).

If you want to filter out all unused groups, a filter is the right decision:

var groups=["admin","moderator","reader","writer"]

var user={
   name:"the user",
   groups:["reader", "writer"]
};

console.log(groups.filter(function(group){
    if (user.groups.indexOf(group)==-1) return true;
}));

Here is the Fiddle.

For the documentation take a loog at MDN Array.prototype.filter

For a future solution with find or findIndex take a look at this fine article.

Edit: For dealing with Objects you could easily adapt the filter function and use a custom comparator function instead indexOf. Here another Fiddle for that case.