Question

我有一个像这样的记录的数据表......

JID                      Date                     RecentChatString
----------------------------------------------------------------------- 
abc@gmail.com         11/Nov/2013 11:53:00        Hi 
abc@gmail.com         11/Nov/2013 11:53:10        Hello 
abc@gmail.com         11/Nov/2013 11:54:00        Good Morning 
def@gmail.com         11/Nov/2013 12:03:00        Ok 
abc@gmail.com         11/Nov/2013 12:05:10        Please reply 
def@gmail.com         11/Nov/2013 12:15:00        Good after noon 
def@gmail.com         11/Nov/2013 12:15:50        Ok bye

我希望按日期排序前10个不同的记录，并且仅表示每个JID的最近聊天..

JID                      Date                     RecentChatString
-----------------------------------------------------------------------
abc@gmail.com         11/Nov/2013 12:05:10        Please reply
def@gmail.com         11/Nov/2013 12:15:50        Ok bye

现在我有这样的代码。我可以使用此代码按日期排序前10条记录。但是，它包含重复的JID's。请帮我。（recent_index是一个DataTable）

DataRow recent_dr = recent_index.NewRow();
recent_dr["JID"] = RosterId;
recent_dr["Date"] = DateTime.Now;
recent_dr["RecentChatString"] = _chatline;
recent_index.Rows.Add(recent_dr);

DataTable dtt = new DataTable("RecentChats");
dtt.Columns.Add("JID", Type.GetType("System.String"));
dtt.Columns.Add("Date", Type.GetType("System.DateTime"));
dtt.Columns.Add("RecentChatString", Type.GetType("System.String"));

IEnumerable<DataRow> recentTen = recent_index.AsEnumerable().OrderByDescending(x=>x["Date"]).Take(10);
recentTen.CopyToDataTable(dtt, LoadOption.OverwriteChanges);

dtt.WriteXml(s + "\\FPhoneData\\chats\\index.xml");

Answer 1

DataTable recentTen = recent_index.AsEnumerable()
    .OrderByDescending(r => r.Field<DateTime>("Date"))
    .GroupBy(r => r.Field<string>("JID"))
    .Take(10)
    .Select(g => g.First())
    .CopyToDataTable();

Answer 2

请尝试以下操作：

DataView view = new DataView(recent_index);
DataTable distinctValues = view.ToTable(true, "JID", "Date" ...);

Answer 3

在您的收藏集上使用.Distinct使用自定义类进行不同的检查

private class DistinctChecker: IEqualityComparer<YourRowType>
{
}

Answer 4

蒂姆的解决方案是正确的。这是声明性查询的替代解决方案：

var latestMessages =
    from r in recent_index.AsEnumerable()
    group r by r.Field<string>("JID") into g
    let latest = g.OrderByDescending(r => r.Field<DateTime>("Date")).First()
    orderby latest.Field<DateTime>("Date")
    select latest;

var recent_dr = latestMessages.Take(10).CopyToDataTable();

如何按日期排序前10个不同的行

4 个答案: