选择与QUOT;定制不同的"使用LINQ列表中的项目 [英] Selecting "custom distinct" items from a List using LINQ

问题描述

我有策略对象的泛型列表。

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 
  

我要选择包含最高policySequence的一行每个policyNumber，让我结束了以下内容：

  ID policyNumber policySequence创建
 3 101 3 CCCC 
 4 102 1 DDDD 
 6 103 2 FFFF 
  

我有以下使用的解决方案的foreach，但不知道是否有这样做的LINQ？

 类节目
 {一种更简单，更清洁的方式
静态无效的主要（字串[] args）
 {
名单，LT;政策与GT; policyList =新的List<政策与GT; 
 {
新政策{ID = 1，policyNumber = 101，policySequence = 1，otherData =AAAA}，
新政策{ID = 2，policyNumber = 101，policySequence = 2， otherData =BBBB}，
新政策{ID = 3，policyNumber = 101，policySequence = 3，otherData =CCCC}，
新政策{ID = 4，policyNumber = 102，policySequence = 1，otherData =DDDD}，
新政策{n = 5，policyNumber = 103，policySequence = 1，otherData =EEEE}，
新政策{ID = 6，policyNumber = 103， policySequence = 2，otherData =FFFF} 
}; 
 
名单，LT;政策与GT; filteredPolicyList =新的List<政策及GT;（）; 
 
的foreach（在policyList VAR政策）
 {
如果（filteredPolicyList.Exists（X =>！x.policyNumber == policy.policyNumber））
 { 
 filteredPolicyList.Add（政策）; 
} 
，否则
 {
 VAR currentPolicyInFilteredList = filteredPolicyList.Where（X => x.policyNumber == policy.policyNumber）。首先（）; 
 
如果（policy.policySequence> currentPolicyInFilteredList.policySequence）
 {
 filteredPolicyList.Remove（currentPolicyInFilteredList）; 
 filteredPolicyList.Add（政策）; 
} 
} 
} 
} 
} 
 
公共类政策
 {
公众诠释身份证; 
公众诠释policyNumber; 
公众诠释policySequence; 
公共字符串otherData; 
} 
  

解决方案

  VAR maxPolicies = policyList 
 .GroupBy（p => p.PolicyNumber）
。选择（GRP => grp.OrderByDescending（p => p.PolicySequence）。首先（）） ; 
  

I have a generic List of Policy objects.

The list contains the following data

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

I want to select the one row containing the highest policySequence for each policyNumber, so that I end up with the following:

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

I have a solution below using a foreach, but was wondering if there was an easier, cleaner way to do this in LINQ?

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;
    }

解决方案

var maxPolicies = policyList
    .GroupBy(p => p.PolicyNumber)
    .Select(grp => grp.OrderByDescending(p => p.PolicySequence).First());

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