c# - 如何按日期排序前 10 个不同的行

Question

我有一个包含这样记录的数据表......

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

我想获得按日期排序的前 10 个不同记录，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的前 10 条记录。但是，它包含重复的 JID 。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();