C# linq 分组依据，排序依据
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linq group by, order by
提问by Nate Pet
I have the following list
我有以下清单
ID Counter SrvID FirstName
-- ------ ----- ---------
1 34 66M James
5 34 66M Keith
3 55 45Q Jason
2 45 75W Mike
4 33 77U Will
What I like to do is to order by ID by ascending and then get the first value of Counter, SrvID which are identical (if any).
我喜欢做的是按 ID 升序排序，然后获取 Counter 的第一个值，SrvID，它们是相同的（如果有）。
So the output would be something like:
所以输出将是这样的：
ID Counter SrvID FirstName
-- ------ ----- ---------
1 34 66M James
2 45 75W Mike
3 55 45Q Jason
4 33 77U Will
Note how ID of 5 is removed from the list as Counter and SrvID was identical to what I had for ID 1 but as ID 1 came first I removed 5.
请注意如何从列表中删除 5 的 ID，因为 Counter 和 SrvID 与我对 ID 1 的相同，但由于 ID 1 首先出现，我删除了 5。
This is what I would do but not working
这是我会做但不工作
var result = (from ls in list1
group ts by new {ls.Counter, ls.SrvID}
order by ls.ID
select new{
ls.ID,
ls.Counter.FirstOrDefault(),
ls.SrvID.First,
ls.FirstName}).ToList()
采纳答案by vc 74
list1.GroupBy(item => new { Counter = item.Counter, SrvID = item.SrvID })
.Select(group => new {
ID = group.First().ID,
Counter = group.Key.Counter,
SrvID = group.Key.SrvID,
FirstName = group.First().FirstName})
.OrderBy(item => item.ID);
回答by Amy B
Group the records up, and pick a winner from each group.
将记录分组，并从每组中选出一名获胜者。
var query =
from record in list1
group record by new {record.Counter, record.SrvID } into g
let winner =
(
from groupedItem in g
order by groupedItem.ID
select groupedItem
).First()
select winner;
var otherQuery = list1
.GroupBy(record => new {record.Counter, record.SrvID })
.Select(g => g.OrderBy(record => record.ID).First());
