C# 使用 LINQ 按键分组并将值发送到列表中
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Group by key and send values into list using LINQ
提问by santosh212
Say I have a simple address class like below:
假设我有一个简单的地址类，如下所示：
public class Address
{
public int AddressId { get; set; }
public List<int> NodeIds { get; set; }
}
and have populated a list of addresses like below:
并填充了如下地址列表：
List<Address> listOfAddresses = new List<Address>
{
new Address {AddressId=1, NodeIds=new List<int>{1}},
new Address {AddressId=2, NodeIds=new List<int>{2}},
new Address {AddressId=3, NodeIds=new List<int>{3}},
new Address {AddressId=1, NodeIds=new List<int>{4}},
new Address {AddressId=1, NodeIds=new List<int>{5}}
}
and I want to group by on AddressIds so the result list will have NodeIds that are essentially rolled up in case of duplicates like below:
我想在 AddressIds 上分组，因此结果列表将包含 NodeIds，这些 NodeIds 基本上会在出现重复的情况下汇总，如下所示：
listOfAddressesWithoutDupes =
AddressId=1, NodeIds=List<int>{1,4,5},
AddressId=2, NodeIds=List<int>{2}},
AddressId=3, NodeIds=new List<int>{3}
so basically I am looking at a groupby function(or something else) that will get me above result
所以基本上我在看一个 groupby 函数（或其他东西），它会让我高于结果
List<Address> listOfFilteredAddresses = listOfAddresses.GroupBy(x=>x.AddressId).Select(y=>new Address{AddressId=y.Key, NodeIds=?});
Thanks in advance..
提前致谢..
采纳答案by dasblinkenlight
You are almost there:
你快到了：
List<Address> listOfFilteredAddresses =
listOfAddresses
.GroupBy(x=>x.AddressId)
.Select(y=>new Address{
AddressId=y.Key
, NodeIds=y.SelectMany(x=>x. NodeIds).ToList()
});
This assumes that NodeIdsin the Addressare unique; if they are not, add Distinct()after SelectMany.
这假设NodeIdsinAddress是唯一的；如果不是，请在Distinct()之后添加SelectMany。
回答by Master Pesho
There is a better way:
有一个更好的方法：
List<Address> listOfFilteredAddresses =
listOfAddresses
.GroupBy(a => a.AddressId)
.Select(g => new Address
{
AddressId = g.Key,
NodeIds = g.ToList()
});
回答by jayanta
You can do by another approach as below
您可以通过以下另一种方法进行
var listOfFilteredAddresses = from e in listOfAddresses
group e by e.AddressId into g
select new
{
AddressID=g.Key,
NodeIDs=g.Select(x=>x.NodeIds).ToList()
};
