LINQ To DataTable

static DataTable dtable = new DataTable();static DataColumn dc = new DataColumn();static DataRow Dr;static void Main(){CreateTable();for (int i = 0; i < 3; i++){Dr = dtable.NewRow();Dr["MId"] = i;Dr["CId"] = i + 1;Dr["FId"] = i + 2;Dr["PId"] = i;dtable.Rows.Add(Dr);}var query = from t in dtable.AsEnumerable()group t by new{Mid = t.Field<Int32>("MId"),PId = t.Field<Int32>("PId")} into gselect new{MId = g.Key.Mid,PId = g.Key.PId};foreach (var v in query){Console.WriteLine("{0} {1}", v.MId, v.PId);}}public static void CreateTable(){//MId CId FId PIddc = new DataColumn("MId", Type.GetType("System.Int32"));dtable.Columns.Add(dc);dc = new DataColumn("CId", Type.GetType("System.Int32"));dtable.Columns.Add(dc);dc = new DataColumn("FId", Type.GetType("System.Int32"));dtable.Columns.Add(dc);dc = new DataColumn("PId", Type.GetType("System.Int32"));dtable.Columns.Add(dc);}

2.按PID分组 获取倒数第二条信息

static DataTable table = new DataTable();static DataColumn dc = new DataColumn();static void Main(){Createtable();table.Rows.Add(1, 2,"2010-1-1");table.Rows.Add(2, 3, "2010-1-1");table.Rows.Add(3, 4, "2010-1-1");table.Rows.Add(4, 5, "2010-1-1");table.Rows.Add(5, 2, "2010-1-2");table.Rows.Add(6, 3, "2010-1-2");table.Rows.Add(7, 4, "2010-1-2");table.Rows.Add(8, 5, "2010-1-2");var query = from dt in table.AsEnumerable()where new int[] { 2, 3, 4 }.Contains(dt.Field<Int32>("PID"))orderby dt.Field<DateTime>("CreateDate") descendinggroup dt by dt.Field<Int32>("PID") into glet n = (from d in g.Take(2).Skip(1) select d).FirstOrDefault()select new{ID = n.Field<Int32>("ID"),PID = g.Key,CreateDate = n.Field<DateTime>("CreateDate")};query.ToList().ForEach(m => Console.WriteLine("{0}\t{1}\t{2}\t",m.ID,m.PID,m.CreateDate));}public static void Createtable(){dc = new DataColumn("ID", Type.GetType("System.Int32"));table.Columns.Add(dc);dc = new DataColumn("PID", Type.GetType("System.Int32"));table.Columns.Add(dc);dc = new DataColumn("CreateDate", Type.GetType("System.DateTime"));table.Columns.Add(dc);}