Linq Group By, Skip 1 其中跳过的 1 是最近的

Question

我有一个存储在事件列表中的对象数据集（变量都已在 class 级别之前声明过）：

    [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 };
    }

我最初只是提取重复项 - 有效（如下）

    [Test]
    public void StoreOnlyDuplicateDetailsFromRowsIntoCollection()
    {
        var duplicates = events.GroupBy(s => s.TableKey)
            .SelectMany(grp => grp.Skip(1)).ToList();

        Assert.AreEqual(2, duplicates.Count);
    }

但是，现在我想提取日期最短的重复项，但我不太确定如何调整我设置的 linq 查询。

这是我到目前为止所做的但是失败了。

如果你想知道 duplicates2 是什么，这是一个失败的尝试：LINQ: Group by aggregate but still get information from the most recent row?

    [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"));
    }

如果您想在 Visual Studio 中尝试不设置接口、classes 等，请参阅此处 https://dotnetfiddle.net/YYoSfM 和 fiddle。基本上如果测试通过，你应该在 'console window'.

中什么也得不到。

Answer 1

您正在跳过第一项，因此这一定是日期最长的一项。为此，您需要在 Skip.

之前使用属于 SelectMany 内的 OrderByDescending

 var duplicates = events
            .GroupBy(s => s.TableKey)
            .SelectMany(grp => grp.OrderByDescending(e => e.EventTime)
                                  .Skip(1))
            .ToList();

如果您希望剩余的重复项按升序排列，只需在 Skip 之后添加一个 .OrderBy(e => e.EventTime)。

哦，你的测试数据是假的。第一个带 PERSON_CODE=1 的数据项是 2013-07-13 但应该在 2013-07-15 才能通过测试套件。

Linq Group By, Skip 1 其中跳过的 1 是最近的

Linq Group By, Skip 1 where the skipped 1 was the most recent

c#

linq

tdd

unit-testing