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[英]LINQ: Group by aggregate but still get information from the most recent row?
[英]Linq Group By, Skip 1 where the skipped 1 was the most recent
我有一個存儲在事件列表中的對象的數據集(所有變量都已在類級別聲明過):
[SetUp]
public void Setup()
{
eventLogObj = new EventLogObj();
event1 = new EventLogObj() { RecordId = 1, TableKey = "PERSON_CODE=1", Status = "S", EventTime = Convert.ToDateTime("2013-07-15 14:00:00") };
event2 = new EventLogObj() { RecordId = 2, TableKey = "PERSON_CODE=2", Status = "S", EventTime = Convert.ToDateTime("2013-07-15 13:00:00") };
event3 = new EventLogObj() { RecordId = 3, TableKey = "PERSON_CODE=3", Status = "S", EventTime = Convert.ToDateTime("2013-07-15 13:00:00") };
event4 = new EventLogObj() { RecordId = 4, TableKey = "PERSON_CODE=2", Status = "S", EventTime = Convert.ToDateTime("2013-07-15 14:00:00") };
event5 = new EventLogObj() { RecordId = 5, TableKey = "PERSON_CODE=1", Status = "S", EventTime = Convert.ToDateTime("2013-07-15 13:00:00") };
events = new List<EventLogObj>() { event1, event2, event3, event4, event5 };
}
我最初只是提取重復項-奏效(下)
[Test]
public void StoreOnlyDuplicateDetailsFromRowsIntoCollection()
{
var duplicates = events.GroupBy(s => s.TableKey)
.SelectMany(grp => grp.Skip(1)).ToList();
Assert.AreEqual(2, duplicates.Count);
}
但是,現在我想提取日期最少的重復項,而且我不太確定如何調整我設置的linq查詢。
這是我到目前為止所做的,但是失敗了。
如果您想知道重復項2是什么,則嘗試實現此操作失敗: LINQ:按匯總分組,但仍從最新行中獲取信息嗎?
[Test]
public void pickDuplicateEventWithLeastDate()
{
var duplicates = events
//.OrderBy(e => e.EventTime)
.GroupBy(s => s.TableKey)
.SelectMany(grp => grp.Skip(1))
.ToList();
var duplicates2 = from res in events
group res by res.TableKey into g
select new
{
Count = g.Count(),
MemberID = g.Key,
MostRecent = g.OrderByDescending(x => x.EventTime)
.First()
};
Assert.AreEqual(2, duplicates.Count);
var e1 = duplicates[0];
var e2 = duplicates[1];
Assert.AreEqual(e1.EventTime, Convert.ToDateTime("2013-07-15 13:00:00"));
Assert.AreEqual(e2.EventTime, Convert.ToDateTime("2013-07-15 13:00:00"));
}
如果您想嘗試而不必在Visual Studio中設置接口,類等,請參見https://dotnetfiddle.net/YYoSfM並進行擺弄。 基本上,如果測試通過,則您在“控制台窗口”中什么也不會獲得。
您正在跳過第一項,因此該日期必須是最高的日期。 為此,您需要使用OrderByDescending
,它位於SelectMany
內部,就在Skip
之前。
var duplicates = events
.GroupBy(s => s.TableKey)
.SelectMany(grp => grp.OrderByDescending(e => e.EventTime)
.Skip(1))
.ToList();
如果您希望將其余重復項按升序排序,只需在Skip
之后添加.OrderBy(e => e.EventTime)
。
哦,您的測試數據是虛假的。 PERSON_CODE=1
的第一個數據項是2013-07-1 3,但應在2013-07-1 5上才能通過測試套件。
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