C#中linq查询机制

//可在后面加上语句　　.count();会立即执行,不会延迟执行

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace Dome_2

{
    class Program
    {
        static void Main(string[] args)
        {
            linqDome5();
           
        }

        #region linq查询机制 

        #region 
        public static void LinqDome6(){

        }
        #endregion

        #endregion

        #region linq 相关练习

        #region linq的方法对字符串的处理
        public static void linqDome6(){
            string[] nums = {"张三","李四","李达","查看及时答复","程思佳","非法","成吉思汗","我不是"};

            var list = nums.Where(x=>x.Length==2).Select(x=>x).GroupBy(x=>x.Substring(0,1));

            

            foreach(var num in list)
            {
                Console.WriteLine("姓====>"+num.Key);

                foreach(var x in num){
                    Console.WriteLine(x);
                }

            }
        }
        #endregion

        #region linq的方法对字符串的处理和排序
        public static void linqDome5(){
            string[] nums = {"张三","李四","车嘎达","车嘎新","查看及时答复","程思佳打击非法","成吉思汗","我不是"};

            var list = nums.Where(x=>x.Length==3).Select(x=>x).GroupBy(x=>x.Substring(0,1));

            foreach(var num in list)
            {
                Console.WriteLine("姓====>"+num.Key);

                foreach(var x in num){
                    Console.WriteLine(x);
                }

            }
        }
        #endregion

        #region linq的方法OrderBy排序
        public static void linqDome4(){
            int[] nums = {1,88,6,7,2,6,5,4,9,13,20};

            //var list = nums.Where(x=>x%2==0).Select(i=>i*i).OrderByDescending(x=>x);  降序

            var list = nums.Where(x=>x%2==0).Select(i=>i*i).OrderBy(x=>x);      //升序

            foreach(var num in list)
            {
                Console.WriteLine(num);
            }
        }
        #endregion

        #region linq的方法where
        public static void linqDome3(){
            int[] nums = {1,7,2,6,5,4,9,13,20};

            var list = nums.Where(x=>x%2==0);

            foreach(var num in list)
            {
                Console.WriteLine(num);
            }
        }
        #endregion

        #region linq的方法select求数组每个数的平方
        public static void linqDome2(){
            int[] nums = {1,7,2,6,5,4,9,13,20};

            var list = nums.Select(x=>x*x);

            foreach(var num in list)
            {
                Console.WriteLine(num);
            }
        }
        #endregion

        #region Linq的基础练习（初识）
        public static void LinqDome(){
             int[] nums = {1,7,2,6,5,4,9,13,20};

            var list = from num in nums where num%2!=0 orderby num descending select num; 
            
            foreach(var num in list)
            {
                Console.WriteLine(num);
            }

            Console.WriteLine("Hello World!");
        }

        #endregion

        #endregion
    }
}