csharp: Linq keyword example

/// <summary>
    /// http://www.dotnetperls.com/linq
    /// </summary>
    public partial class LinqForm : Form
    {

        const int _max = 1000000;
        /// <summary>
        /// Linq keyword
        /// </summary>
       public enum  CheckLinq
        {
            Distinct,
            Union,
            Intersect,
            Except,
            Var,
            Loop,
            New,
            Orderby,
            Group,
            Join,
            Let,
            Where,
            ToDictionary,
            Lambda,
            GroupJoin,
            GroupBy
        }
        /// <summary>
        ///
        /// </summary>
        /// <returns></returns>
       DataTable setcom()
       {
           DataTable dt = new DataTable();
           dt.Columns.Add("id", typeof(int));
           dt.Columns.Add("name", typeof(string));
           dt.Rows.Add(1, "Distinct");
           dt.Rows.Add(2, "Union");
           dt.Rows.Add(3, "Intersect");
           dt.Rows.Add(4, "Except");
           dt.Rows.Add(5, "Var");
           dt.Rows.Add(6, "Loop");
           dt.Rows.Add(7, "New");
           dt.Rows.Add(8, "Orderby");
           dt.Rows.Add(9, "Group");
           dt.Rows.Add(10, "Join");
           dt.Rows.Add(11, "Let");
           dt.Rows.Add(12, "Where");
           dt.Rows.Add(13, "ToDictionary");
           dt.Rows.Add(14, "Lambda");
           dt.Rows.Add(15, "GroupJoin");
           dt.Rows.Add(16, "GroupBy");

           return dt;
       }

        /// <summary>
        ///
        /// </summary>
        public LinqForm()
        {
            InitializeComponent();
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void LinqForm_Load(object sender, EventArgs e)
        {
            this.comboBox1.DataSource = setcom();
            this.comboBox1.ValueMember = "id";
            this.comboBox1.DisplayMember = "name";

        }

        /// <summary>
        ///
        /// </summary>
        public  string TestSetSemantics(CheckLinq check)
        {
            List<string> lstColumn = new List<string>();
            List<string> strDistinct = new List<string>();
            List<string> strUnion = new List<string>();
            List<string> strExcept = new List<string>();
            List<string> strIntersect = new List<string>();
            List<string> strVar = new List<string>();
            List<string> strLoop = new List<string>();
            List<string> strNew = new List<string>();
            List<string> strOrderby = new List<string>();
            List<string> strGroup = new List<string>();
            List<string> strJoin = new List<string>();
            List<string> strLet = new List<string>();
            List<string> strWhere = new List<string>();
            List<string> strToDictionary = new List<string>();
            List<string> strLambda = new List<string>();
            List<string> strGroupJoin = new List<string>();
            List<string> strGroupBy = new List<string>();

            string str = string.Empty;

            string[] dailySecurityLog = {
                   "Bob logged in",
                   "Bob logged out",
                   "Bob logged in",
                   "Bill logged in",
                   "Melissa logged in",
                   "Bob logged out",
                   "Bill logged out",
                   "Bill logged in",
                   "Tim logged in",
                   "Scott logged in",
                   "Scott logged out",
                   "Dave logged in",
                   "Tim logged out",
                   "Bob logged in",
                   "Dave logged out"};

            Employee[] project1 = {
                       new Employee(){ Name = "Bob" },
                       new Employee(){ Name = "Bill" },
                       new Employee(){ Name = "Melissa" },
                       new Employee(){ Name = "Shawn" } };
            Employee[] project2 = {
                       new Employee(){ Name = "Shawn" },
                       new Employee(){ Name = "Tim" },
                       new Employee(){ Name = "Scott" } };
            Employee[] project3 = {
                       new Employee(){ Name = "Bob" },
                       new Employee(){ Name = "Dave" },
                       new Employee(){ Name = "Tim" },
                       new Employee(){ Name = "Shawn" } };
            IEnumerable<string> whoLoggedIn =
                  dailySecurityLog.Where(logEntry => logEntry.Contains("logged in")).Distinct();
            var allProjectEmployees = project1.Union(project2.Union(project3));

            switch (check)
            {
                case CheckLinq.Distinct:
                    // Distinct
                    //"Everyone who logged in today:";
                    foreach (string who in whoLoggedIn)
                    {
                        strDistinct.Add(who);
                    }
                     str=String.Join(",",strDistinct.ToArray()); //结果：Bob logged in,Bill logged in,Melissa logged in,Tim logged in,Scott logged in,Dave logged in
                    break;
                case CheckLinq.Union:
                    // Union
                    //"Employees for all projects:";
                    foreach (Employee employee in allProjectEmployees)
                    {
                        strUnion.Add(employee.Name);

                    }
                    str = String.Join(",",strUnion.ToArray());  //结果：Bob,Bill,Melissa,Shawn,Tim,Scott,Dave
                    break;
                case CheckLinq.Intersect:
                    // Intersect
                    //"Employees on every project:";

                    var everyProjectEmployees = project1.Intersect(project2.Intersect(project3));
                    foreach (Employee employee in everyProjectEmployees)
                    {
                        strIntersect.Add(employee.Name);
                    }
                    str = String.Join(",",strIntersect.ToArray()); //结果：Shawn
                    break;
                case CheckLinq.Except:

                    // Except
                    var intersect1_3 = project1.Intersect(project3);
                    var intersect1_2 = project1.Intersect(project2);
                    var intersect2_3 = project2.Intersect(project3);
                    var unionIntersect = intersect1_2.Union(intersect1_3).Union(intersect2_3);

                    //"Employees on only one project:";
                    var onlyProjectEmployees = allProjectEmployees.Except(unionIntersect);
                    foreach (Employee employee in onlyProjectEmployees)
                    {
                        strExcept.Add(employee.Name);
                    }
                    str = String.Join(",",strExcept.ToArray()); //结果：Bill,Melissa,Scott,Dave
                    break;
                case CheckLinq.Var:
                    int[] array = { 1, 2, 3, 6, 7, 8 };
	                // Query expression.
	                var elements = from element in array
		                       orderby element descending
		                       where element > 2
		                       select element;
	                // Enumerate.
	                foreach (var element in elements)
	                {
                        strVar.Add(element.ToString());
	                }
                    str = String.Join(",", strVar.ToArray());
                    break;
                case CheckLinq.Loop:
                    int[] values = { 10, 0, 1, 1, 20, 300, 400, 4 };
	                // Version 1: use LINQ.
	                var s1 = Stopwatch.StartNew();
	                for (int i = 0; i < _max; i++)
	                {
	                    int count = CountLinq(values);
	                }
	                s1.Stop();

	                // Version 2: use for-loop.
	                var s2 = Stopwatch.StartNew();
	                for (int i = 0; i < _max; i++)
	                {
	                    int count = CountFor(values);
	                }
	                s2.Stop();
	                strLoop.Add(((double)(s1.Elapsed.TotalMilliseconds * 1000000) /
	                    _max).ToString("0.00 ns"));
	                strLoop.Add(((double)(s2.Elapsed.TotalMilliseconds * 1000000) /
	                    _max).ToString("0.00 ns"));
                    str = String.Join(",", strLoop.ToArray());
                    break;
                case CheckLinq.New:
                        string[] newarray = { "one", "two", "three", "four", "", "seven" };
	                    // Use Select New.
                        var result = from newelement in newarray
                                     select new { Value = newelement, Id = Id(newelement) };

	                    foreach (var anonymous in result)
	                    {
	                        string value = anonymous.Value;
	                        int id = anonymous.Id;
	                        strNew.Add(anonymous.ToString());
	                    }
                        str = String.Join(",", strNew.ToArray());
                    break;
                case CheckLinq.Orderby:
                    // Input array.
                    int[] orderarray = { 2, 5, 3 };
                    // Use orderby, orderby ascending, and orderby descending.
                    var result0 = from orderelement in orderarray
                                  orderby orderelement
                                  select orderelement;

                    var result1 = from orderelement in orderarray
                                  orderby orderelement ascending
                                  select orderelement;

                    var result2 = from orderelement in orderarray
                                  orderby orderelement descending
                                  select orderelement;
                    // Print results.
                    strOrderby.Add("result0:");
                    foreach (var orderelement in result0)
                    {
                        strOrderby.Add(orderelement.ToString());
                    }
                    strOrderby.Add("result1:");
                    foreach (var orderelement in result1)
                    {
                        strOrderby.Add(orderelement.ToString());
                    }
                    strOrderby.Add("result2:");
                    foreach (var orderelement in result2)
                    {
                        strOrderby.Add(orderelement.ToString());
                    }
                    str = String.Join(",", strOrderby.ToArray());
                    break;
                case CheckLinq.Group:
                    // Input array.
                    int[] grouparray = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

                    // Group elements by IsEven.
                    var groupresult = from groupelement in grouparray
                                      orderby groupelement
                                      group groupelement by IsEven(groupelement);

                    // Loop over groups.
                    foreach (var group in groupresult)
                    {
                        // Display key and its values.
                        strGroup.Add(group.Key.ToString());
                        foreach (var value in group)
                        {
                            strGroup.Add(value.ToString());
                        }
                    }
                    str = String.Join(",", strGroup.ToArray());
                    break;
                case CheckLinq.Join:
                       // Example customers.
                       var customers = new Customer[]
	                    {
	                        new Customer{ID = 5, Name = "Sam"},
	                        new Customer{ID = 6, Name = "Dave"},
	                        new Customer{ID = 7, Name = "Julia"},
	                        new Customer{ID = 8, Name = "Sue"}
	                    };

                                        // Example orders.
                                        var orders = new Order[]
	                    {
	                        new Order{ID = 5, Product = "Book"},
	                        new Order{ID = 6, Product = "Game"},
	                        new Order{ID = 7, Product = "Computer"},
	                        new Order{ID = 8, Product = "Shirt"}
	                    };

                    // Join on the ID properties.
                    var query = from c in customers
                                join o in orders on c.ID equals o.ID
                                select new { c.Name, o.Product };

                    // Display joined groups.
                    foreach (var group in query)
                    {
                        strJoin.Add(string.Format("{0} bought {1}", group.Name, group.Product));
                    }
                    str = String.Join(",", strJoin.ToArray());
                    break;
                case CheckLinq.Let:
                    int[] letarray = { 0, 1, 2 };
	                // Build IEnumerable of Analyze arguments and its return values.
                    var letresult = from letelement in letarray
                                    let v = Analyze(letelement)
		                     let x = Analyze(v)
		                     select new { v, x };
	                // This prints argument, return value pairs.
                    foreach (var letelement in letresult)
	                {
                        strLet.Add(letelement.ToString());
	                }
                    str = String.Join(",", strLet.ToArray());

                    break;
                case CheckLinq.Where:
                    //
                    // Example array that contains unwanted null and empty strings.
                    //
                    string[] wherearray = { "dot", "", "net", null, null, "perls", null };
                    //
                    // Use Where method to remove null strings.
                    //
                    strWhere.Add("Begins output from first loop:");
                    var whreresult1 = wherearray.Where(item => item != null);
                    foreach (string value in whreresult1)
                    {
                        strWhere.Add(value);
                    }
                    //
                    // Use Where method to remove null and empty strings.
                    //
                    strWhere.Add("Begins output from second loop:");
                    var whrereresult2 = wherearray.Where(item => !string.IsNullOrEmpty(item));
                    foreach (string value in whrereresult2)
                    {
                        strWhere.Add(value);
                    }
                    str = String.Join(",", strWhere.ToArray());

                    break;
                case CheckLinq.ToDictionary:
                    // Example with strings and List.
                    List<string> list = new List<string>()
	                {
	                    "cat",
	                    "dog",
	                    "animal"
	                };
                    var animals = list.ToDictionary(x => x, x => true);
                    if (animals.ContainsKey("dog"))
                    {
                        // This is in the Dictionary.
                        strToDictionary.Add("dog exists");
                    }
                    str = String.Join(",", strToDictionary.ToArray());//结果：dog exists
                    break;
                case CheckLinq.Lambda:
                    List<int> lamelements = new List<int>() { 10, 20, 31, 40 };
	                // ... Find index of first odd element.
                    int oddIndex = lamelements.FindIndex(x => x % 2 != 0);  //
                         strLambda.Add(oddIndex.ToString());
                    str = String.Join(",", strLambda.ToArray());//结果：31 index: 2
                    break;
                case CheckLinq.GroupJoin:
                    // Example customers.
	                var gcustomers = new Customer[]
	                {
	                    new Customer{Code = 5, Name = "Sam"},
	                    new Customer{Code = 6, Name = "Dave"},
	                    new Customer{Code = 7, Name = "Julia"},
	                    new Customer{Code = 8, Name = "Sue"}
	                };

	                // Example orders.
	                var gorders = new Order[]
	                {
	                    new Order{KeyCode = 5, Product = "Book"},
	                    new Order{KeyCode = 6, Product = "Game"},
	                    new Order{KeyCode = 7, Product = "Computer"},
	                    new Order{KeyCode = 7, Product = "Mouse"},
	                    new Order{KeyCode = 8, Product = "Shirt"},
	                    new Order{KeyCode = 5, Product = "Underwear"}
	                };

	                // Correlate "customers" with "orders"
	                // ... Use Code property as key for Customer.
	                // ... Use KeyCode property as key for Order.
	                // ... For each result, create object with Name and IEnumerable of orders.
	                var gquery = gcustomers.GroupJoin(gorders,
	                    c => c.Code,
	                    o => o.KeyCode,
	                    (c, gresult) => new Result(c.Name, gresult));

	                // Enumerate results.
	                foreach (var gresult in gquery)
	                {
                        string gj = string.Empty;
                        List<string> gp = new List<string>();
	                    gj=string.Format("{0} bought...", gresult.Name);
	                    foreach (var item in gresult.Collection)
	                    {
		                   gp.Add(item.Product);
	                    }
                        gj = gj + String.Join(",",gp.ToArray());
                        strGroupJoin.Add(gj);
                        gj = "";
	                }
                    str = String.Join(";", strGroupJoin.ToArray()); //结果：Sam bought...Book,Underwear;Dave bought...Game;Julia bought...Computer,Mouse;Sue bought...Shirt
                    break;
                case CheckLinq.GroupBy:
                    // Input array.
                    int[] gyarray = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
                    // Group elements by IsEven.
                    var gyresult = gyarray.GroupBy(a => IsEven(a));
                    // Loop over groups.
                    foreach (var group in gyresult)
                    {
                        string gb = string.Empty;
                        // Display key for group.
                        gb=string.Format("IsEven = {0}:", group.Key);

                        List<string> gbv = new List<string>();
                        // Display values in group.
                        foreach (var value in group)
                        {
                            gbv.Add(string.Format("{0} ", value));
                        }
                        gb =gb+ String.Join(",", gbv.ToArray());
                        // End line.
                        strGroupBy.Add(gb);
                        gb = "";
                    }
                    str = String.Join(";", strGroupBy.ToArray()); //结果：IsEven = False:1 ,3 ,5 ,7 ,9 ;IsEven = True:2 ,4 ,6 ,8
                    break;
                default:
                    str = "";
                    break;                  

            }
            return str;

        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="values"></param>
        /// <returns></returns>
        int CountLinq(int[] values)
        {
            // Count values greater than or equal to 10 with LINQ.
            return (from x in values
                    where x >= 10
                    select x).Count();
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="values"></param>
        /// <returns></returns>
        int CountFor(int[] values)
        {
            // Count values greater than or equal to 10 with a loop.
            int count = 0;
            for (int i = 0; i < values.Length; i++)
            {
                if (values[i] >= 10)
                {
                    count++;
                }
            }
            return count;
        }

         int _value;
        /// <summary>
        ///
        /// </summary>
        /// <param name="element"></param>
        /// <returns></returns>
         int Id(string element)
        {
            // Get Id.
            return string.IsNullOrEmpty(element) ?
                0 :
                _value++;
        }
         /// <summary>
         /// 奇数偶数
         /// </summary>
         /// <param name="value"></param>
         /// <returns></returns>
         bool IsEven(int value)
         {
             return value % 2 == 0;
         }
        /// <summary>
        ///
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
         int Analyze(int value)
         {
             // Return a value for each argument.
             switch (value)
             {
                 case 0:
                     return 1;
                 case 1:
                     return 2;
                 case 2:
                 default:
                     return 3;
             }
         }
        /// <summary>
        ///
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button1_Click(object sender, EventArgs e)
        {
            int c = (int)this.comboBox1.SelectedValue;
            switch (c)
            {
                case 1:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Distinct);
                    break;
                case 2:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Union);
                    break;
                case 3:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Intersect);
                    break;
                case 4:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Except);
                    break;
                case 5:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Var);
                    break;
                case 6:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Loop);
                    break;
                case 7:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.New);
                    break;
                case 8:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Orderby);
                    break;
                case 9:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Group);
                    break;
                case 10:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Join);
                    break;
                case 11:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Let);
                    break;
                case 12:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Where);
                    break;
                case 13:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.ToDictionary);
                    break;
                case 14:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.Lambda);
                    break;
                case 15:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.GroupJoin);
                    break;
                case 16:
                    this.textBox1.Text = TestSetSemantics(CheckLinq.GroupBy);
                    break;
                default:
                    this.textBox1.Text = "";
                    break;
            }
        }
    }

    class Customer
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public int Code { get; set; }
    }

    class Order
    {
        public int ID { get; set; }
        public string Product { get; set; }
        public int KeyCode { get; set; }
    }

    class Result
    {
        public string Name { get; set; }
        public IEnumerable<Order> Collection { get; set; }
        public Result(string name, IEnumerable<Order> collection)
        {
            this.Name = name;
            this.Collection = collection;
        }
    }

 /// <summary>
    ///
    /// </summary>
    public class Employee
    {
        /// <summary>
        ///
        /// </summary>
        public string Name { get; set; }
        /// <summary>
        ///
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return this.Name;
        }
        /// <summary>
        ///
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public override bool Equals(object obj)
        {
            return this.GetHashCode().Equals(obj.GetHashCode());
        }
        /// <summary>
        ///
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
            return this.Name.GetHashCode();
        }
    }