如何使用LINQ筛选一组

Question

的最大我有这个名单

var commonContractsList = (
     from i in referredDilutions 
     join f in dilutionsList 
      on i.Contract equals f.Contract 
     select f) 
    .ToList(); 

名单commonContractsList有几个字段和三个特别contract，instalment和amount。我们可以有几个instalment s一个contract。每个contract/instalment有一个amount。

现在，我想要做的是得到，对于每个contract，获取contract s的所有记录的列表，其中instalment具有更高的amount。

源数据

contract instalment amount 
1   1    100 
1   2    1000 
2   1    100 
3   1    1000 
4   1    200 
4   2    100 
5   1    1000 

所以我需要，

结果

contract instalment amount 
1   2    1000 
2   1    100 
3   1    1000 
4   1    200 
5   1    1000 

我对linq的知识有限，而且我在项目中遇到困难。

任何想法？

Answer 1

下面的代码应该给你预期的结果：

var data = new[] 
{ 
    new { contract = 1, installment = 1, amount = 100}, 
    new { contract = 1, installment = 2, amount = 1000}, 
    new { contract = 2, installment = 1, amount = 100}, 
    new { contract = 3, installment = 1, amount = 1000}, 
    new { contract = 4, installment = 1, amount = 200}, 
    new { contract = 4, installment = 2, amount = 100}, 
    new { contract = 5, installment = 1, amount = 1000}, 
}; 

var result = from d in data 
      group d by d.contract into g 
      let highestInstallment = (from x in g 
             orderby x.amount descending 
             select x).First() 
      select new 
      { 
       contract = g.Key, 
       installment = highestInstallment.installment, 
       amount = highestInstallment.amount 
      }; 

您按contract，然后各组内，你检查的最高金额。我添加了let子句，因此您不必重复installment和amount的子查询。

Answer 2

修改那些公认的答案谁寻找简约的例子：

var data = new[] 
{ 
    new { contract = 1, installment = 1, amount = 100}, 
    new { contract = 1, installment = 2, amount = 1000}, 
    new { contract = 2, installment = 1, amount = 100}, 
    new { contract = 3, installment = 1, amount = 1000}, 
    new { contract = 4, installment = 1, amount = 200}, 
    new { contract = 4, installment = 2, amount = 100}, 
    new { contract = 5, installment = 1, amount = 1000}, 
}; 

这给了相同的结果（在另外没有必要选择）：

var result1 = from d in data 
      group d by d.contract 
      into g 
      select (from x in g 
        orderby x.amount descending 
        select x).First(); 

同样的是一个LINQ方法写入链（一行代码）：

var result2 = data.GroupBy(d => d.contract).Select(g => g.OrderByDescending(x => x.amount).First()); 

将接受的答案改写为od链（无论如何，但让它在这里）

var result3 = data.GroupBy(d => d.contract) 
       .Select(g => new {g, highestInstallment = (g.OrderByDescending(x => x.amount)).First()}) 
       .Select(@t => new 
       { 
        contract = @t.g.Key, 
        installment = @t.highestInstallment.installment, 
        amount = @t.highestInstallment.amount 
       });