Linq分组功能

Linq在集合操作上很方便,很多语法都借鉴自sql,但linq的分组却与sql有一定的区别,故整理发布如下。 1.  Linq分组 分组后以Key属性访问分组键值。 每一组为一个IEnumberAble或IQeuryAble的集合,可以继续枚举。 Sample:


 string[] World = { "Hello","World"}; string[] Brother = { "Hello","Brother"}; var result = from wld in World from bth in Brother group new { wld, bth } by new { wld, bth }.bth; OR var result = from wld in World from bth in Brother group new { wld, bth } by bth;
foreach (var obj in result) { foreach (var ct in obj) { Response.Write(ct.wld + ct.bth); } }

说明:在linq里面,group by 和groupby是两个不同的概念,前者标识分组,后者标识排序。分组时如不特意制定select,则将分组后的结果作为结果集。

2.   Linq排序后,分组再排序


    public class Student      {          public string Name = "";          public string Sex = "";          public int Age;      }
Student[] stAry = { new Student{ Name ="Jon1",Sex="female",Age =21}, new Student{ Name ="Jon2",Sex="male",Age =22}, new Student{ Name ="Jon3",Sex="male",Age =33}, new Student{ Name ="Jon4s",Sex="female",Age =44}, new Student{ Name ="Jon5",Sex="female",Age =25}, new Student{ Name ="Jon6",Sex="female",Age =26} }; var c = from st in stAry orderby st.Age group st by st.Sex into temp orderby temp.Key ascending select temp;

概要说明: Linq查询后产生的结果集和sql类似,如果涉及到多个查询则会产生一个多“列”的集合用以“select”,如果用到linq的分组功能,则分组后的结果将作为一个“集合”,而这个集合可以在他所在的查询中作为一个源被查询,也可以当做一个元素被直接“select”。如下例所示。注意:Into在linq里面也用以分组,产生的结果用来查询,当然,不用这个结果也不会错。

3.  join分组:

        int[] Ary1 = { 1, 23, 45, 67, 8, 4, 4 };          int[] Ary2 = { 23, 1, 1,5, 67, 4 };
var c = from A1 in Ary1 join A2 in Ary2 on A1 equals A2 into VAL2 select VAL2;

左外连接:

        var c = from A1 in Ary1                  join A2 in Ary2 on A1 equals A2 into VAL2                  from a2 in VAL2. DefaultIfEmpty(int.MinValue)                   select new {A1,a2,VAL2};

注:DefaultIfEmpty(int.MinValue)表示集合为空的时候,用指定的默认值关联前面的集合。如果不指定,则由于集合为空,A1找不到关联的对象将不产生相应的行。

4.linq嵌套查询   查询某个数据集中不全为null或“”的列

            var c = from DataColumn dc in ds.Tables[0].Columns                      where ( from dr in dt.AsEnumerable()                              where !dr.IsNull(dc)                                  select dr                                  ).Any()                      select dc;

5.分组后统计

                var groupedApply901 = (from y in arrInput
group y by new { y.UnavailableType, y.FlowType } into z
select new CashBagUnavailableShare
{
UnavailableType = z.Key.UnavailableType,
FlowType = z.Key.FlowType,
UnavailableVol = z.Sum(s => s.UnavailableVol), }).ToList<CashBagUnavailableShare>();

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