using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int[] numbers = {5, 3, 4, 8 ,9 ,33};

        var getTheNumbers = from number in numbers

                            where number < 5

                            select number;

        List<int> newNumbers = new List<int>();

        foreach(var number in numbers)

        {

            if(number < 5)

            {

                newNumbers.Add(number);

            }

        }           

        System.Console.WriteLine(string.Join(" , ", getTheNumbers));

        System.Console.WriteLine(string.Join(" , ", newNumbers));

        List<int> numbersList = getTheNumbers.ToList();

        numbersList.ForEach(n => Console.WriteLine("Numbers: " + n));

        Console.WriteLine(" ");

        Console.WriteLine(" ");

        Console.WriteLine("Grouping");

        List<Person> people = GetPeople();

        Console.WriteLine(" ");

        Console.WriteLine("Grouping By Gender:");

        Console.WriteLine(" ");

        var groupedByGender = from p in people

                             group p by p.Gender;

        foreach(var p in groupedByGender)

        {

        Console.WriteLine(p.Key);

            foreach(var person in p)

            {

            Console.WriteLine(string.Format("Name: {0} - Gender: {1} - Age {2} ",person.Name, person.Gender, person.Age) );

            }

        }

        Console.WriteLine(" ");

        Console.WriteLine(" ");

        Console.WriteLine("Grouping By Age , over 21:");

        Console.WriteLine(" ");

        var overTwentyOnes = from p in people

                            where p.Age > 21

                            group p by p.Age;

        foreach(var p in overTwentyOnes)

        {

        Console.WriteLine(p.Key);

            foreach(var person in p)

            {

            Console.WriteLine(string.Format("Name: {0} - Gender: {1} - Age {2} ",person.Name, person.Gender, person.Age) );

            }

        }   

        Console.WriteLine(" ");

        Console.WriteLine("Grouping By First Letter of Name:");

        Console.WriteLine(" ");

        var alphaGroup = from p in people

                        orderby p.Name

                        group p by p.Name[0];

            foreach(var p in alphaGroup)

        {

        Console.WriteLine(p.Key);

            foreach(var person in p)

            {

            Console.WriteLine(string.Format("Name: {0} - Gender: {1} - Age {2} ",person.Name, person.Gender, person.Age) );

            }

        }   

        Console.WriteLine(" ");

        Console.WriteLine(" ");

        Console.WriteLine("LINQ METHOD SYNTAX:");

        Console.WriteLine(" ");

        var alphaBeticGroup = people.OrderBy(p => p.Name).GroupBy(p => p.Name[0]);

            foreach(var p in alphaBeticGroup)

            {

                Console.WriteLine(p.Key);

​

                foreach(var person in p)

                {

                Console.WriteLine(string.Format("Name: {0} - Gender: {1} - Age {2} ",person.Name, person.Gender, person.Age) );

                }           

            }   

        Console.WriteLine(" ");

        Console.WriteLine(" ");

        Console.WriteLine("LINQ METHOD SYNTAX, Grouping By Multiple Keys (Gender, Age):");

        Console.WriteLine(" ");

        var multiKey = people.GroupBy(p => new { p.Gender, p.Age}).OrderBy(p => p.Count());

        foreach(var p in multiKey)

            {

                Console.WriteLine(p.Key);

​

                foreach(var person in p)

                {

                Console.WriteLine(string.Format("Name: {0}",person.Name) );

                }           

            }   

    }

public enum Gender { Male, Female } 

    public class Person

    {       

    public string Name {get;set;}

    public int Age {get;set;}

    public int Height {get;set;}        

    public Gender Gender {get;set;} 

    }

    public static List<Person> GetPeople()

    {

    var people = new List<Person>

    {

    new Person { Name = "Tom", Age = 20, Height = 180,  Gender = Gender.Male  },

        new Person { Name = "Dick", Age = 20, Height = 185,  Gender = Gender.Male  },

        new Person { Name = "Harry", Age = 19, Height = 170,  Gender = Gender.Male  },

        new Person { Name = "Jane", Age = 21, Height = 170,  Gender = Gender.Female  },

        new Person { Name = "Wendy", Age = 20, Height = 173,  Gender = Gender.Female  },

        new Person { Name = "Susan", Age = 23, Height = 179,  Gender = Gender.Female  },

    };

    return people;

    }

}