Difference between two lists

Question

I Have two generic list filled with CustomsObjects.

I need to retrieve the difference between those two lists(Items who are in the first without the items in the second one) in a third one.

I was thinking using .Except() was a good idea but I don't see how to use this.. Help!

Answer 1

var third = first.Except(second);

(you can also call ToList() after Except(), if you don't like referencing lazy collections.)

The Except() method compares the values using the default comparer, if the values being compared are of base data types, such as int, string, decimal etc.

Otherwise the comparison will be made by object address, which is probably not what you want... In that case, make your custom objects implement IComparable (or implement a custom IEqualityComparer and pass it to the Except() method).

Answer 2

        List<int> list1 = new List<int>();
        List<int> list2 = new List<int>();
        List<int> listDifference = new List<int>();

        foreach (var item1 in list1)
        {
            foreach (var item2 in list2)
            {
                if (item1 != item2)
                    listDifference.Add(item1);
            }
        }

Answer 3

You could do something like this:

var result = customlist.Where(p => !otherlist.Any(l => p.someproperty == l.someproperty));

Answer 4

Since the Except extension method operates on two IEumerables, it seems to me that it will be a O(n^2) operation. If performance is an issue (if say your lists are large), I'd suggest creating a HashSet from list1 and use HashSet's ExceptWith method.

Answer 5

If both your lists implement IEnumerable interface you can achieve this using LINQ.

list3 = list1.where(i => !list2.contains(i));

Answer 6

List<ObjectC> _list_DF_BW_ANB = new List<ObjectC>();    
List<ObjectA> _listA = new List<ObjectA>();
List<ObjectB> _listB = new List<ObjectB>();

foreach (var itemB in _listB )
{     
    var flat = 0;
    foreach(var itemA in _listA )
    {
        if(itemA.ProductId==itemB.ProductId)
        {
            flat = 1;
            break;
        }
    }
    if (flat == 0)
    {
        _list_DF_BW_ANB.Add(itemB);
    }
}