C# 选择"；“定制独特”；使用LINQ从列表中删除项目

我有一个策略对象的通用列表

该列表包含以下数据

id  policyNumber   policySequence  otherData
1   101            1               aaaa
2   101            2               bbbb
3   101            3               cccc
4   102            1               dddd
5   103            1               eeee
6   103            2               ffff

我想为每个policyNumber选择一行，其中包含最高的policySequence，这样我就可以得到以下结果：

id  policyNumber   policySequence  created
3   101            3               cccc
4   102            1               dddd
6   103            2               ffff

下面我有一个使用foreach的解决方案，但我想知道在LINQ中是否有更简单、更干净的方法来实现这一点

class Program
    {
        static void Main(string[] args)
        {
            List<Policy> policyList = new List<Policy>
                                          {
                                              new Policy {id = 1, policyNumber = 101, policySequence = 1, otherData = "aaaa"},
                                              new Policy {id = 2, policyNumber = 101, policySequence = 2, otherData = "bbbb"},
                                              new Policy {id = 3, policyNumber = 101, policySequence = 3, otherData = "cccc"},
                                              new Policy {id = 4, policyNumber = 102, policySequence = 1, otherData = "dddd"},
                                              new Policy {id = 5, policyNumber = 103, policySequence = 1, otherData = "eeee"},
                                              new Policy {id = 6, policyNumber = 103, policySequence = 2, otherData = "ffff"}
                                          };

            List<Policy> filteredPolicyList = new List<Policy>();

            foreach(var policy in policyList)
            {
                if(!filteredPolicyList.Exists(x => x.policyNumber == policy.policyNumber))
                {
                    filteredPolicyList.Add(policy);
                }
                else
                {
                    var currentPolicyInFilteredList = filteredPolicyList.Where(x => x.policyNumber == policy.policyNumber).First();

                    if (policy.policySequence > currentPolicyInFilteredList.policySequence)
                    {
                        filteredPolicyList.Remove(currentPolicyInFilteredList);
                        filteredPolicyList.Add(policy);
                    }
                }
            }
        }
    }

    public class Policy
    {
        public int id;
        public int policyNumber;
        public int policySequence;
        public string otherData;
    }

类程序
{
静态void Main（字符串[]参数）
{
列表策略列表=新列表
{
新策略{id=1，policyNumber=101，policySequence=1，otherData=“aaaa”}，
新策略{id=2，policyNumber=101，policySequence=2，otherData=“bbbbbb”}，
新策略{id=3，policyNumber=101，policySequence=3，otherData=“cccc”}，
新策略{id=4，policyNumber=102，policySequence=1，otherData=“dddddd”}，
新策略{id=5，policyNumber=103，policySequence=1，otherData=“eeee”}，
新策略{id=6，policyNumber=103，policySequence=2，otherData=“ffff”}
};
List filteredpolycylist=新列表（）；
foreach（保单列表中的var策略）
{
如果（！filteredPolicyList.Exists（x=>x.policyNumber==policy.policyNumber））
{
filteredPolicyList.Add（策略）；
}
其他的
{
var currentPolicyInfiledList=filteredPolicyList.Where（x=>x.policyNumber==policy.policyNumber）.First（）；
如果（policy.policySequence>currentPolicyInFilteredList.policySequence）
{
FilteredPolycylist.Remove（CurrentPolicyInfiledList）；
filteredPolicyList.Add（策略）；
}
}
}
}
}
公共阶级政策
{
公共int id；
公共政策编号；
公共政策序列；
公共字符串数据；
}

如果使用LINQ to对象，可以使用项目的

DistinctBy

方法：

var maxPolicies = policyList.OrderByDescending(x => x.PolicySequence)
                            .DistinctBy(x => x.PolicyNumber);

---

您可以分组和聚合：

var result = from p in policyList
             group p by p.policyNumber into g
             select new { Policy = g.Key, Max = g.Max() };

---

给那些发现这个问题的人的一个提示。如果您想按多个条件分组。GroupBy（p=>new{p.criteria，p.criteria1，p.criteria2，}）

var result = from p in policyList
             group p by p.policyNumber into g
             select new { Policy = g.Key, Max = g.Max() };