• C# LINQ 基本操作实例


    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    
    namespace First_exam
    {
        class Student
        {
            /// <summary>
            ///学生姓名的字段和属性
            /// </summary>
            private string _Name;
            public string Name
            {
                get { return this._Name; }
            }
            private string _Xingbie;
            /// <summary>
            /// 学生性别的字段和属性
            /// </summary>
            public string Xingbie
            {
                get { return this._Xingbie; }
            }
            /// <summary>
            /// 学生年龄的字段和属性
            /// </summary>
            private uint _Age;
            public uint Age
            {
                get { return this._Age; }
            }
            /// <summary>
            /// 学生成绩的字段和属性
            /// </summary>
            private List<LessonScore> _Scores;
            public List<LessonScore> Scores
            {
                get { return this._Scores; }
            }
            /// <summary>
            /// 构造函数,传入学生姓名,性别,年龄,成绩
            /// </summary>
            public Student(string name, string xb, uint age, List<LessonScore> scrs)
            {
                this._Name = name;
                this._Xingbie = xb;
                this._Age = age;
                this._Scores = scrs;
            }
            public Student(string name, string xb, uint age)
            {
                this._Name = name;
                this._Xingbie = xb;
                this._Age = age;
                this._Scores = null;
            }
            public override string ToString()
            {
                string str;
                str = string.Format("{0}--{1}--{2}",this._Name, this._Age,this._Xingbie);
                return str;
            }
    
        }
    
        class LessonScore
        {
            /// <summary>
            /// 课程成绩的字段和属性
            /// </summary>
            private float _Score;
            public float Score
            {
                get { return this._Score; }
            }
            /// <summary>
            /// 课程名称的字段和属性
            /// </summary>
            private string _Lessson;
            public string Lesson
            {
                get { return this._Lessson; }
            }
            /// <summary>
            /// 构造函数
            /// </summary>
            public LessonScore(string les, float scr)
            {
                this._Lessson = les;
                this._Score = scr;
            }
    
            public override string ToString()
            {
                string str;
                str = string.Format("{0}----{1}分", this._Lessson,this._Score);
                return str;
            }
        }
        class Program
        {
            static void Main(string[] args)
            {
                Student[] arr = 
                {
                    new Student("张氏那","",20),
                    new Student("李四","",23),
                    new Student("李霞","",23),
                    new Student("王妈妈","",25),
                    new Student("郭明","",22),
                    new Student("欧阳夏","",24),
                    new Student("王丹","",20),
                    new Student("张宝","",25),
                };
    
                var query =
                    from val in arr
                    select val;
                foreach (Student item in query)
                {
                    Console.WriteLine(item);
                }
                Console.WriteLine();
    
                var query2 =
                    from val in arr
                    select val.Name;
                foreach(string item in query2)
                {
                    Console.Write("{0},   ",item);
                }
                Console.WriteLine();
                Console.WriteLine();
    
                var query3 =
                    from val in arr
                    select val.Name.Length;
                foreach (int item in query3)
                {
                    Console.Write("{0},   ", item);
                }
                Console.WriteLine();
                Console.WriteLine();
    
                var query4 =
                    from val in arr
                    select new { val.Name, val.Age,  NameLen = val.Name.Length};
                foreach(var item2 in query4)
                {
                    Console.WriteLine(item2);
                }
                Console.WriteLine();
                
                int[] ary = { 9,54,32,1,67,43,0,9,7,4,9,2,23,66,61};
                var query5 =
                    from val in ary
                    orderby val
                    select val;
                foreach(var item in query5)
                {
                    Console.Write("{0}   ",item);
                }
                Console.WriteLine();
                Console.WriteLine();
                var query6 =
                    from val in ary
                    orderby val descending
                    select val;
                foreach (var item in query6)
                {
                    Console.Write("{0}   ", item);
                }
                Console.WriteLine();
                Console.WriteLine();
    
    
                var query7 =
                    from val in arr
                    orderby val.Name.Length ascending, val.Age descending
                    select val;
                foreach(var item in query7)
                {
                    Console.WriteLine(item);
                }
                Console.WriteLine();
    
                var query8 =
                    from val in arr
                    group val by val.Xingbie;
                foreach(var grp in query8)
                {
                    Console.WriteLine(grp.Key);
                    foreach(var st in grp)
                    {
                        Console.WriteLine("	{0}",st);
                    }
                }
                Console.WriteLine();
    
                var query9 =
                    from val in arr
                    group val by val.Age into stgrp
                    orderby stgrp.Key descending
                    select stgrp;
                foreach(var st in query9)
                {
                    Console.WriteLine("{0}岁的学生:",st.Key);
                    foreach(var stu in st)
                    {
                        Console.WriteLine("	{0}",stu);
                    }
                }
                Console.WriteLine();
                Console.WriteLine("**************************************************************************"); 
                Console.WriteLine();
    
                /*
                 *from子句的复合查询 
                 */
                Student[] stAry = { 
                                      new Student("张氏那","",20, 
                                          new List<LessonScore>{
                                              new LessonScore("语文",80.5f),
                                              new LessonScore("数学",90f),
                                              new LessonScore("英语",89f)
                                          }),
                                      new Student("李四","",23,
                                          new List<LessonScore>{
                                              new LessonScore("语文",86.5f),
                                              new LessonScore("数学",97f),
                                              new LessonScore("英语",95f)
                                          }),
                                      new Student("李霞","",23,
                                          new List<LessonScore>{
                                              new LessonScore("语文",76f),
                                              new LessonScore("数学",85f),
                                              new LessonScore("英语",79f)
                                          }),
                                      new Student("王妈妈","",25,
                                          new List<LessonScore>{
                                              new LessonScore("语文",85f),
                                              new LessonScore("数学",87f),
                                              new LessonScore("英语",79f)
                                          }),
                                      new Student("郭明","",22,
                                          new List<LessonScore>{
                                              new LessonScore("语文",69f),
                                              new LessonScore("数学",72f),
                                              new LessonScore("英语",83f)
                                          }),
                                      new Student("欧阳夏","",24,
                                          new List<LessonScore>{
                                              new LessonScore("语文",85f),
                                              new LessonScore("数学",85f),
                                              new LessonScore("英语",79f)
                                          }),
                                      new Student("王丹","",20,
                                          new List<LessonScore>{
                                              new LessonScore("语文",73f),
                                              new LessonScore("数学",77f),
                                              new LessonScore("英语",80f)
                                          }),
                                      new Student("张宝","",25,
                                          new List<LessonScore>{
                                              new LessonScore("语文",88f),
                                              new LessonScore("数学",89f),
                                              new LessonScore("英语",94f)
                                          }), 
                                  };
    
                var query10 =
                    from st in stAry
                    from scr in st.Scores
                    where scr.Score > 80
                    group new { st.Name, scr } by st.Name;
                foreach(var grp in query10)
                {
                    Console.WriteLine(grp.Key);
                    foreach(var item in grp)
                    {
                        Console.WriteLine("	{0}",item);
                    }
                }
    
                Console.WriteLine();
                Console.WriteLine("**************************************************************************");
                Console.WriteLine();
                int[] intarry1 = { 5,10,15,20,25,50,30,33,100};
                int[] intarry2 = { 10,20,30,40,50,60,70,80,90,100};
                var query11 =
                    from val1 in intarry1
                    from val2 in intarry2
                    where val2 % val1 == 0
                    group val2 by val1;
                foreach(var grp in query11)
                {
                    Console.Write("{0}:  ",grp.Key);
                    foreach(var val in grp)
                    {
                        Console.Write("{0}  ",val);
                    }
                    Console.WriteLine();
                }
    
                Console.WriteLine();
                Console.WriteLine("*********************join*****************************************");
                Console.WriteLine();
                Console.WriteLine("**********内部联接**************************");
                int[] intarray1 = { 5,15,25,30,33,40};
                int[] intarray2 = { 10,20,30,40,50,60,70,80,90,100};
                var query12 =
                    from val1 in intarray1
                    join val2 in intarray2 on val1 % 5 equals val2 % 15
                    select new { VAL1 = val1,VAL2 = val2};
                foreach(var val in query12)
                {
                    Console.WriteLine(val);
                }
    
                Console.WriteLine();
                Console.WriteLine("**********分组联接**************************");
    
                var query13 =
                    from val1 in intarray1
                    join val2 in intarray2 on val1 % 5 equals val2 % 15 into grpName
                    select new { VAL1 = val1, VAL2 = grpName};
                foreach(var val in query13)
                {
                    Console.Write("{0}:  ",val.VAL1);
                    foreach(var obj in val.VAL2)
                    {
                        Console.Write("{0}  ",obj);
                    }
                    Console.WriteLine();
                }
    
                Console.WriteLine();
                Console.WriteLine("**********左外部联接**************************");
                var query14 =
                    from val1 in intarray1
                    join val2 in intarray2 on val1 % 5 equals val2 % 15 into grpName
                    from grp in grpName.DefaultIfEmpty()
                    select new { VAL1 = val1 , VAL2 = grp};
                foreach(var val in query14)
                {
                    Console.WriteLine(val);
                }
            }
        }
    }
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  • 原文地址:https://www.cnblogs.com/crandy/p/4546126.html
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