LINQ 基本子句之一 (select/where/group/into)
特别喜欢同事看到我写了一句小排序的时候说,他当然喜欢Linq了,虽然我只是baidu之,不知其然也不知其所以然。
基本格式 var<变量> = from <项目> in <数据源> where <表达式> orderby <表达式> select <项目>
1. from & select
static void Main(string[] args)
{
string[] abc = { "a3", "af", "de" };
var result = from a in abc
select a;
foreach (var r in result)
{
Console.WriteLine(r);
}
Console.ReadLine();
}
from为必须子句,select不必须。
多个from子句
static void Main(string[] args) { string[] abc = { "a3", "af", "de" }; string[] de = { "af","de" }; var result = from a in abc from d in de where a.Contains(d) select a; foreach (var r in result) { Console.WriteLine(r); } Console.ReadLine(); }
2.where
where表示条件,也可有多个。或者省略where用&&连接
static void Main(string[] args) { string[] abc = { "a3", "aff", "de" }; string[] de = { "af","de" }; var result = from a in abc from d in de where a.Contains(d) && a.Length>2 //where a.Length>2 select a; foreach (var r in result) { Console.WriteLine(r); } Console.ReadLine(); }
3.order by
ascending/descending 默认 ascending
static void Main(string[] args) { string[] abc = { "a3", "aff", "de" }; string[] de = { "af","de" }; var result = from a in abc from d in de where a.Contains(d) orderby a.Length descending select a; foreach (var r in result) { Console.WriteLine(r); } Console.ReadLine(); }
4.group by
在LINQ中,group对from语句进行分组,返回元素类型为IGrouping<TKey,TElement>的对象序列,因此每个返回需再次循环。
如下:
static void Main(string[] args) { string[] xyz = { "a", "bc", "def" }; var x = from o in xyz group o by o.Length; foreach (var m in x) { Console.Write(m.Key); foreach (var p in m) Console.WriteLine(p); } Console.ReadLine(); }
注意 group的语法为group x by y, 同时group在使用时,末尾没有select。
5. into
INTO 创建临时标识符用于保存查询的集合。
static void Main(string[] args) { string[] xyz = { "a", "bc", "def" }; var x = from o in xyz group o by o[0] into z select z; foreach (var m in x) { Console.Write(m.Key); foreach (var p in m) Console.WriteLine(p); } Console.ReadLine(); }
我知道这个例子略显神经,可是白痴的我还没发现into语句究竟干嘛用,也许,明天的明天,我就会发现了。
因为——只要在路上,总会遇到庆典~