一. C#从1.0到4.0, 随着Linq,泛型的支持，代码越来越简单优雅
int[] nums = { , , , , , , , , , };
IEnumerable<int> newNums = from n in nums where n > select n;
newNums = newNums.Where(new Func<int,int, bool>(delegate(int i,int index) { return i < index; }));
newNums = newNums.Where(new Func<int, int, bool>((int i, int index)=> i < index));
newNums = newNums.Where(delegate(int i, int index) { return i < index; });
newNums = newNums.Where((i, index) => i < index);
foreach (var i in newNums)
{
Console.WriteLine(i);
}
二.集合操作，也可适于到EF的数据库操作
1.创建两个实体类
public class Store
{
public string Id;
public string Name;
}
public class Person
{
public string name { get; set; }
public int age { get; set; }
public string StoreId { get; set; }
}
2.插入数据
var Stores = new List<Store>()
{
new Store() { Id="",Name="1班"},
new Store() { Id="",Name="2班"}
}; var Persons = new List<Person>()
{
new Person() { name="p1",age=, StoreId=""},
new Person() { name="p2",age=, StoreId=""},
new Person() { name="p3",age=, StoreId=""},
new Person() { name="p4",age=, StoreId=""},
new Person() { name="p5",age=, StoreId=""},
new Person() { name="p6",age=, StoreId=""},
new Person() { name="p7",age=, StoreId=""},
new Person() { name="p8",age=, StoreId=""}
};
3. 查询年龄小于3岁的人1班和2班分别有几个人
var plst = Persons.Where(o => o.age > ).GroupBy(o => o.StoreId).Select(g => new { StoreId = g.Key, Count = g.Count() }).Join(Stores, s => s.StoreId, p => p.Id, (s, p) => new { s.StoreId, storeName = p.Name, s.Count });
foreach (var p in plst)
{
Console.WriteLine(p.storeName + "有" + p.Count + "个人");
}
4.输出
2班有2个人
1班有3个人