datatable使用lambda

Lamdba是延迟执行的，实际上什么都没有发生，当真正使用对象的时候（例如调用：First, Single, ToList….的时候）才执行。

1.Where
var var_dtTable = dtTable.AsEnumerable().Where<DataRow>(W => W["NAME"].ToString()=="张三");
int count = var_dtTable.Count<DataRow>();//获取dtTable中NAME为张三的个数

2.Average
//获取dtTable中avg_name列的平局数
int avg = dtTable.AsEnumerable().Average<DataRow>(A => float.Parse(A["avg_name"].ToString()))

3.GroupBy
DataTable dtTable = new DataTable();//数据源
DataTable dtResult = new DataTable();
dtResult.Columns.Add("groupBy_name", typeof(string));
dtResult.Columns.Add("sum_name", typeof(int));
dtResult.Columns.Add("count_name", typeof(int));
var var_dtTable= dtTable.AsEnumerable().GroupBy(G => G["groupBy_name"].ToString()).Select(S => new {
                groupBy_name= s.Key,//获取分组的值
                sum_name= s.Sum(m => m.Field<int>("sum_name")),//获取列名为sum_name数据的和
                count_name= s.Count(m => m.Field<int>("count_name"))//获取列名为count_name数据的个数
                });
var_dtTable.ToList().ForEach(f=> dtResult.Rows.Add(f.groupBy_name,f.sum_name,f.count_name);//对应的顺序为dtResult列的顺序

4.OrderBy
DataTable dtTable = new DataTable();//数据源
dtTable = dtTable.AsEnumerable().OrderByDescending(o => o["OrderBy_name"]).CopyToDataTable();//降序
dtTable = dtTable.AsEnumerable().OrderBy(o => o["OrderBy_name"]).CopyToDataTable();//升序

5.Distinct
DataTable dtTable = new DataTable();//数据源
//column_name是要Distinct列的名字
dtTable = dtTable.AsEnumerable().Distinct(new ColumnEquals("column_name")).CopyToDataTable();

 var erpBOMList = dt.AsEnumerable().GroupBy(G => new { t1 = G["Main_PartNo"], t2 = G["Material_PartNo"], t3 = G["Material_PartName"], t4 = G["Material_Qty"] })
                .Select(s => new Mes_ERP_MaterialBOM
                {

                    Main_PartNo = s.Max(m => m.Field<string>("Main_PartNo")),
                    Material_PartNo = s.Max(m => m.Field<string>("Material_PartNo")),
                    Material_PartName = s.Max(m => m.Field<string>("Material_PartName")),
                    Material_Qty = s.Max(m => m.Field<decimal>("Material_Qty")),
                }).ToList();