C# LINQ查询表达式及对应LAMBDA表达式的用法

//以下为例子中涉及查询的数据
List<Student> stu = new List<Student>()
{
　　new Student(){Id = 1,Name = "王同学",Age = 24},
　　new Student(){Id = 2,Name = "王同学",Age = 30},
　　new Student(){Id = 3,Name = "王同学",Age = 21},
　　new Student(){Id = 4,Name = "赵同学",Age = 20},
　　new Student(){Id = 5,Name = "钱同学",Age = 22},
　　new Student(){Id = 6,Name = "孙同学",Age = 23},
　　new Student(){Id = 7,Name = "周同学",Age = 23},
　　 new Student(){Id = 8,Name = "吴同学",Age = 20},
　　new Student(){Id = 9,Name = "郑同学",Age = 25},
　　new Student(){Id = 10,Name = "蒋同学",Age = 26}
};

//查询年龄是30岁的王同学的信息
var res = from t in stu
    where t.Name == "王同学" && t.Age == 30
    select t;

//对应的Lambda表达式
//var res1 = stu.Where(t => t.Age == 30 && t.Name == "王同学");

foreach (var item in res)//显示查询结果
{
    Console.Write("学号:"+item.Id+"\n姓名:"+item.Name+"\n年龄:"+item.Age);
}

//查询年龄是30岁的王同学的信息
var res = from t in stu
    where t.Name == "王同学" && t.Age == 30
    select t;
//var res1 = stu.Where(t => t.Age == 30 && t.Name == "王同学");Lambda表达式写法

foreach (var item in res)
{
    Console.Write("学号:"+item.Id+"\n姓名:"+item.Name+"\n年龄:"+item.Age);
}

Console.WriteLine("\n--------------------------------------------------------------------------");

stu.Add(new Student(){Id = 11,Name = "王同学",Age = 30});

foreach (var item in res)
{
    Console.Write("学号:" + item.Id + "\n姓名:" + item.Name + "\n年龄:" + item.Age);
    Console.WriteLine();
}

//从学生中选出年龄小于25岁并且按照年龄降序排列
var res = from t in stu
    where t.Age < 25
    orderby t.Age descending
    select t;
//var res1 = stu.Where(t => t.Age < 25).OrderByDescending(t => t.Age).Select(t => t);Lambda写法

foreach (var item in res)
{
    Console.Write("学号:" + item.Id + "\n姓名:" + item.Name + "\n年龄:" + item.Age);
    Console.WriteLine();
}

//从学生中查询姓王的同学的信息并且按照年龄降序排列
var res = from t in stu
    from n in t.Name
    where n == '王'//名字中带有王字
    orderby t.Age descending
    select t;
//var res1 = stu.Where(t => t.Name.IndexOf("王") == 0).OrderByDescending(t => t.Age);lambda表达式

foreach (var item in res)
{
    Console.Write("学号:" + item.Id + "\n姓名:" + item.Name + "\n年龄:" + item.Age);
    Console.WriteLine();
}

//参数越靠前，优先级越高
//先按age排序，当分数相同时再按id排序...依次类推

 var res = from t in stu
    orderby t.Age, t.Id
    select t;
//var res1 = stu.OrderBy(t => t.Age).ThenBy(t => t.Id);Lambda表达式

foreach (var item in res)
{
    Console.Write("学号:" + item.Id + "\n姓名:" + item.Name + "\n年龄:" + item.Age);
    Console.WriteLine();
}

//按照年龄进行分组,查询相同年龄数量大于2的内容
var res = from t in stu
    group t by t.Age into s
    where s.Count()>=2
    select s;
//var res1 = stu.GroupBy(t => t.Age).Where(s => s.Count() >= 2);lambda表达式

foreach (var item in res)
{
    foreach (var items in item)
    {
        Console.Write("学号:" + items.Id + "\n姓名:" + items.Name + "\n年龄:" + items.Age);
        Console.WriteLine();
    }
    Console.WriteLine();
}

List<s> pSt = new List<s>();
pSt.Add(new s() { year = 1999, name = "小张" });
pSt.Add(new s() { year = 2000, name = "小王" });
pSt.Add(new s() { year = 2001, name = "小李" });
pSt.Add(new s() { year = 2010, name = "小赵" });
List<school> pSc = new List<school>();
pSc.Add(new school() { year = 1999, name = "aaa" });
pSc.Add(new school() { year = 2001, name = "bbb" });
pSc.Add(new school() { year = 2002, name = "ccc" });
pSc.Add(new school() { year = 2010, name = "ddd" });
pSc.Add(new school() { year = 2012, name = "fff" });

var res = from t1 in pSc
     from t2 in pSt
    where t1.year == t2.year
    select new {year = t1.year, name = t1.name + t2.name};

foreach (var item in res)
{
    Console.Write("年:" + item.year + "姓名:" + item.name);
    Console.WriteLine();
}

Console.WriteLine("开始构造大数组...");
//构造大数组
const int count = 100000000;
var data = new int[count];
var r = new Random();
for (int i = 0; i < count; i++)
{
    data[i] = r.Next(40);
}
Console.WriteLine("开始计算...");
var st = System.DateTime.Now;
var sum = (from x in data where x > 20 select x).Sum();//常规linq-耗时1.8641s
var st2 = System.DateTime.Now;
var sum2 = (from x2 in data.AsParallel() where x2 > 20 select x2).Sum();//并行查询-耗时0.6620s

 //var sum3 = data.AsParallel().Where(x3 => x3 > 20).Sum();//或并行查询----x3 => x3 > 20（Lambda表达式）
var st3 = System.DateTime.Now;

 

var sum4 = (from c in System.Collections.Concurrent.Partitioner.Create(data, true).AsParallel() where c > 20 select c).Sum();

var dt1 = st2 - st;
var dt2 = st3 - st2;
Console.WriteLine("常规linq耗时：{0}s", dt1.TotalSeconds.ToString());
Console.WriteLine("并行linq耗时：{0}s", dt2.TotalSeconds.ToString());
Console.ReadKey();