LInq 与lambda表达式
LinQ是我们常用的技术之一。因为我们绕不开的要对数据进行一系列的调整，如 排序、 条件筛选、求和、分组、多表联接 等等。
lambda则是我们常用的语法糖，配合linq使用天衣无缝，不知不觉就用上了，主要还是看着代码简洁，逼格够高。。。
接下来我们就来看看常用的有哪些
先来点基础数据
//用户类
public class User
{
[DataMember]
public int ID { get; set; }
[DataMember]
public string Name { get; set; }
[DataMember]
public string Address { get; set; }
[DataMember]
public string Phone { get; set; }
[DataMember]
public string Sex { get; set; } [DataMember]
public int Age { get; set; }
[DataMember]
public int SchID { get; set; }
}
/// <summary>
/// 学校类
/// </summary>
internal class School {
public int SchID { get; set; }
public string SchName { get; set; }
public School(){}
public School(int id,string name)
{
SchID = id;
SchName = name;
}
}
/// <summary>
/// 公司类
/// </summary>
internal class Company {
public string Name { get; set; }
public List<User> Users { get; set; }
public Company() { }
public Company(string name, List<User> list)
{
Name = name;
Users = list;
}
}
接下来初始化点测试数据
User user1 = new User()
{
ID = 111,
Name = "张一",
Address = "上海市某某区",
Phone = "13547878787",
Age = 30,
Sex = "男",
SchID=1
};
User user2 = new User()
{
ID = 112,
Name = "李小二",
Address = "上海市某某区",
Phone = "13547878783",
Age = 30,
Sex = "女",
SchID = 1
};
User user3 = new User()
{
ID = 113,
Name = "张三",
Address = "上海市某某区",
Phone = "13547878784",
Age = 30,
Sex = "男",
SchID = 1
};
User user4 = new User()
{
ID = 114,
Name = "李四",
Address = "上海市某某区",
Phone = "13547878785",
Age = 30,
Sex = "男",
SchID = 1
};
List<User> userlist = new List<User>(4) { user1, user2, user3, user4 };
List<School> Schlist = new List<School>() {
new School(1,"武汉大学"),new School(2,"华中科技大学"),new School(3,"华中师范大学")
};
统计（求和）Sum
//求和
var sum = userlist.Where(a => { return a.ID > 0; }).Sum(a=>a.ID);
Console.WriteLine(sum);
//另一种写法
sum =(from a in userlist where a.ID>0 select a.ID ).Sum();
Console.WriteLine(sum);
IEnumerable.Where()方法里面的参数数委托类型Func<TSource, bool> 前面为参数 最后面一个为返回值
求最大最小值 Max Min
//求最大值
var max = userlist.Max(a => a.ID);
Console.WriteLine(max);
//最小值
var min = userlist.Min(a => a.ID);
Console.WriteLine(min);
循环 ForEach
//循环输出
userlist.ForEach(a =>
{
if (a.Age > 20)
{
Console.WriteLine(a.ID);
} });
条件筛选 where
//筛选
var user = userlist.Where(a => a.ID == 114).Single();
//筛选所有男性用户
var templist = userlist.Where(a => a.Sex == "男").ToList();
排序
//排序 根据ID逆序
templist = userlist.OrderByDescending(a => a.ID).ToList();
//升序
templist = userlist.OrderBy(a => a.ID).ToList();
分组 ToLookup 和 GroupBy
//分组
var lookup = userlist.ToLookup(a => a.Sex);
foreach (var item in lookup)
{
Console.WriteLine(item.Key);
foreach (var sub in item)
{
Console.WriteLine("\t\t"+sub.Name+" "+sub.Age);
}
}
//另一种
var dic = userlist.GroupBy(a => a.Sex);
foreach (var item in dic)
{
Console.WriteLine(item.Key);
foreach (var sub in item)
{
Console.WriteLine("\t\t" + sub.Name + " " + sub.Age);
}
}
联接 （这里只展示内联接）Join
//联接
var temp = from usertemp in userlist join sch in Schlist on usertemp.SchID equals sch.SchID
select new { Id = usertemp.ID, Name = usertemp.Name, Age = usertemp.Age,Schname=sch.SchName };
返回的匿名类，也可以指点实体类
类型查找 OfType
类型查找很少用到 因为我们都是用的泛型，不过这里还是列出来看看
//类型查找
List<object>objlist =new List<object>(){1,"2",false,"s",new User(){ID=1,Name="xx"}}; IEnumerable<string> query1 = objlist.OfType<string>(); foreach (string fruit in query1)
{
Console.WriteLine(fruit);
}
可以看到把2个字符串类型给查找出来了
查找深层嵌套 SelectMany
selectMany很少人用也比较少人知道，它可以避免多层嵌套循环 其使用场景还是挺多的，见下代码
//查找深层嵌套
//初始化数据 Company ChinaMobile = new Company("中国移动",userlist);
Company ChinaUnicom = new Company("中国联通", userlist);
List<Company> companylist = new List<Company>() { ChinaMobile, ChinaUnicom };
//找出2个公司所有女性成员
var selectlist = companylist.SelectMany(a => a.Users).Where(b => b.Sex == "女");
foreach (var item in selectlist)
{
Console.WriteLine(item.Name+":"+item.Sex);
}
这里可以看到 给出的数据源都是同一个list集合 然后我们看每个集合中只有一个女性成员
正常情况下要想取得这数据的话 要经过2层嵌套循环
foreach (Company c in companylist)
{ foreach (var item in c.Users)
{
if (item.Sex == "女")
{
Console.WriteLine(item.Name + ":" + item.Sex);
}
}
}
分类: C#知识体系
标签: Linq lambda