Difference and intersection of two arrays containing objects

Question

I have two arrays list1 and list2 which have objects with some properties; userId is the Id or unique property:

list1 = [
    { userId: 1234, userName: 'XYZ'  }, 
    { userId: 1235, userName: 'ABC'  }, 
    { userId: 1236, userName: 'IJKL' },
    { userId: 1237, userName: 'WXYZ' }, 
    { userId: 1238, userName: 'LMNO' }
]

list2 = [
    { userId: 1235, userName: 'ABC'  },  
    { userId: 1236, userName: 'IJKL' },
    { userId: 1252, userName: 'AAAA' }
]

I'm looking for an easy way to execute the following three operations:

1. list1 operation list2 should return the intersection of elements:

   [
       { userId: 1235, userName: 'ABC'  },
       { userId: 1236, userName: 'IJKL' }
   ]
   

2. list1 operation list2 should return the list of all elements from list1 which don't occur in list2:

   [
       { userId: 1234, userName: 'XYZ'  },
       { userId: 1237, userName: 'WXYZ' }, 
       { userId: 1238, userName: 'LMNO' }
   ]
   

3. list2 operation list1 should return the list of elements from list2 which don't occur in list1:

   [
       { userId: 1252, userName: 'AAAA' }
   ]
   

Answer 1

This is the solution that worked for me.

 var intersect = function (arr1, arr2) {
            var intersect = [];
            _.each(arr1, function (a) {
                _.each(arr2, function (b) {
                    if (compare(a, b))
                        intersect.push(a);
                });
            });

            return intersect;
        };

 var unintersect = function (arr1, arr2) {
            var unintersect = [];
            _.each(arr1, function (a) {
                var found = false;
                _.each(arr2, function (b) {
                    if (compare(a, b)) {
                        found = true;    
                    }
                });

                if (!found) {
                    unintersect.push(a);
                }
            });

            return unintersect;
        };

        function compare(a, b) {
            if (a.userId === b.userId)
                return true;
            else return false;
        }