如何删除两个列表之一 <object> 基于对象属性的项目？

Question

I have a list which has items that are similar but have different createdOn dates. I want to only keep the items with same displayName but the latest createdOn date. I have created a predicate to compare list items based on displayName, so I'm able to find if I have an item with the same displayName, but I'm not sure how do I find the other item with older createdOn date and remove it.

The predicate

public bool Equals(Obj x, Obj y)
        {
            if (x == null && y == null) { return true; }
            if (x == null || y == null) { return false; }

            return x.DisplayName == y.DisplayName;
        }

        public int GetHashCode(Obj obj)
        {
            if (obj == null || obj.DisplayName == null) { return 0; }
            return obj.DisplayName.GetHashCode();
        }

The RemoveDuplicateMethod:

public static List<Obj> RemoveDuplicatesSet(List<Obj> items, ValueComparer valueComparer)
    {
        // Use HashSet to maintain table of duplicates encountered.
        var result = new List<Obj>();
        var set = new HashSet<Obj>(valueComparer);
        for (int i = 0; i < items.Count; i++)
        {
            // If not duplicate, add to result.
            if (!set.Contains(items[i]))
            {
                result.Add(items[i]);
                // Record as a future duplicate.
                set.Add(items[i]);
            }
        }
        return result;
    }

Any ideas?

Answer 1

Well, i'd use it in this way:

List<Obj> items = items
    .GroupBy(x => x.Id) // or DisplayName, question is unclear
    .Select(g => g.OrderByDescending(x => x.CreatedOn).First())
    .ToList();

You could also pass your comparer to GroupBy , although i don't know ValueComparer , if it implements IEqualityComparer<Obj> it works.

Answer 2

I don't know the data you have but try using LINQ.

var dItems = items.Distinct();

And if you want only lastest ones use lambda expression.

var dItems = items.OrderByDescending(x => x.createdOn).Distinct();