c# - 从通用列表底部删除重复项

Question

我正在尝试从通用列表底部删除重复项。我的类定义如下

public class Identifier
{
    public string Name { get; set; }
}

我定义了另一个实现 IEqualityComparer 的类来从列表中删除重复项

public class DistinctIdentifierComparer : IEqualityComparer<Identifier>
{
    public bool Equals(Identifier x, Identifier y)
    {
        return x.Name == y.Name;
    }

    public int GetHashCode(Identifier obj)
    {
        return obj.Name.GetHashCode();
    }
}

但是，我正在尝试删除旧项目并保留最新项目。例如，如果我有如下定义的标识符列表

Identifier idn1 = new Identifier { Name = "X" };
Identifier idn2 = new Identifier { Name = "Y" };
Identifier idn3 = new Identifier { Name = "Z" };
Identifier idn4 = new Identifier { Name = "X" };
Identifier idn5 = new Identifier { Name = "P" };
Identifier idn6 = new Identifier { Name = "X" };

List<Identifier> list =  new List<Identifier>();
list.Add(idn1);
list.Add(idn2);
list.Add(idn3);
list.Add(idn4);
list.Add(idn5);
list.Add(idn6);

我已经实现了

var res = list.Distinct(new DistinctIdentifierComparer());

如何通过使用 distinct 来确保我保留了 idn6 并删除了 idn1 和 idn4？

Answer 1

Most LINQ operators are order-preserving :Distinct() 的 API 表示它将获取遇到的每个项目的第一个实例。如果您想要最后一个实例，只需执行以下操作:

var res = list.Reverse().Distinct(new DistinctIdentifierComparer());

另一个可以避免您必须定义显式比较器的选项是:

var res = list.GroupBy(i => i.Name).Select(g => g.Last());

来自 MSDN:

The IGrouping objects are yielded in an order based on the order of the elements in source that produced the first key of each IGrouping. Elements in a grouping are yielded in the order they appear in source.