Csharp/CSharp Tutorial/Data Structure/IEnumerable

Counting Enumerable

using System;
using System.Collections;
using System.Collections.Generic;
using System.ruponentModel;
        class CountingEnumerable : IEnumerable<int>
        {
            public IEnumerator<int> GetEnumerator()
            {
                return new CountingEnumerator();
            }
            IEnumerator IEnumerable.GetEnumerator()
            {
                return GetEnumerator();
            }
        }
        class CountingEnumerator : IEnumerator<int>
        {
            int current = -1;
            public bool MoveNext()
            {
                current++;
                return current < 10;
            }
            public int Current
            {
                get { return current; }
            }
            object IEnumerator.Current
            {
                get { return Current; }
            }
            public void Reset()
            {
                throw new NotSupportedException();
            }
            public void Dispose()
            {
            }
        }
    class MainClass
    {

        static void Main()
        {
            CountingEnumerable counter = new CountingEnumerable();
            foreach (int x in counter)
            {
                Console.WriteLine(x);
            }
        }
    }

Get list of integer whose value is higher than 10

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using System.Xml.Linq;
    class Program
    {
        static void Main(string[] args)
        {
            int[] integers = { 1, 6, 2, 27};
            
            IEnumerable<int> twoDigits = from numbers in integers where numbers >= 10 select numbers;
            Console.WriteLine("Integers > 10:");
            foreach (var number in twoDigits)
            {  
               Console.WriteLine(number);
            }
        }
    }

Implement IEnumerable with loop

using System;
using System.Collections.Generic;
using System.Text;
class MyClass : IEnumerable<string>
{
   IEnumerator<string> Letter
   {
      get
      {
         string[] s = { "A", "B", "C" };
         for (int i = 0; i < s.Length; i++)
            yield return s[i];
      }
   }
   public IEnumerator<string> GetEnumerator()
   {
      return Letter;
   }
   System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
   {
      return Letter;
   }
}
class MainClass
{
   static void Main()
   {
      MyClass mc1 = new MyClass();
      foreach (string s in mc1)
         Console.Write("{0} ", s);
   }
}

A B C

Implement IEnumerable with "yield"

using System;
using System.Collections.Generic;
using System.Text;
class MyClass : IEnumerable<string>
{
   IEnumerator<string> Letter
   {
      get
      {
         yield return "A";
         yield return "B";
         yield return "C";
      }
   }
   public IEnumerator<string> GetEnumerator()
   {
      return Letter;
   }
   System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
   {
      return Letter;
   }
}
class MainClass
{
   static void Main()
   {
      MyClass mc1 = new MyClass();
      foreach (string s in mc1)
         Console.Write("{0} ", s);
   }
}

A B C

Iterator Block Iteration Sample

using System;
using System.Collections;
using System.ruponentModel;
    class IteratorBlockIterationSample : IEnumerable
    {
        object[] values;
        int startingPoint;
        public IteratorBlockIterationSample(object[] values, int startingPoint)
        {
            this.values = values;
            this.startingPoint = startingPoint;
        }
        public IEnumerator GetEnumerator()
        {
            for (int index = 0; index < values.Length; index++)
            {
                yield return values[(index + startingPoint) % values.Length];
            }
        }
        static void Main()
        {
            object[] values = { "a", "b", "c", "d", "e" };
            IteratorBlockIterationSample collection = new IteratorBlockIterationSample(values, 3);
            foreach (object x in collection)
            {
                Console.WriteLine(x);
            }
        }
    }

Provide different IEnumerable implemetation for one class

using System;
using System.Collections.Generic;
public class Employee
{
    public string Name;
    public string Title;
    public Employee(string name, string title)
    {
        Name = name;
        Title = title;
    }
    public override string ToString()
    {
        return string.Format("{0} ({1})", Name, Title);
    }
}
public class EmployeeList 
{
    private List<Employee> employeeList = new List<Employee>();
    public IEnumerator<Employee> GetEnumerator()
    {
        foreach (Employee tm in employeeList)
        {
            yield return tm;
        }
    }
    public IEnumerable<Employee> Reverse
    {
        get
        {
            for (int c = employeeList.Count - 1; c >= 0; c--)
            {
                yield return employeeList[c];
            }
        }
    }
    public IEnumerable<Employee> FirstTwo
    {
        get
        {
            int count = 0;
            foreach (Employee tm in employeeList)
            {
                if (count >= 2)
                {
                    yield break;
                }
                else
                {
                    count++;
                    yield return tm;
                }
            }
        }
    }
    public void AddEmployee(Employee member)
    {
        employeeList.Add(member);
    }
}
public class MainClass
{
    public static void Main()
    {
        EmployeeList employeeList = new EmployeeList();
        employeeList.AddEmployee(new Employee("A", "AA"));
        employeeList.AddEmployee(new Employee("B", "BB"));
        employeeList.AddEmployee(new Employee("C", "CC"));
        
        Console.WriteLine("Enumerate using default iterator:");
        foreach (Employee member in employeeList)
        {
            Console.WriteLine("  " + member.ToString());
        }
        Console.WriteLine("Enumerate using the FirstTwo iterator:");
        foreach (Employee member in employeeList.FirstTwo)
        {
            Console.WriteLine("  " + member.ToString());
        }
        Console.WriteLine("Enumerate using the Reverse iterator:");
        foreach (Employee member in employeeList.Reverse)
        {
            Console.WriteLine("  " + member.ToString());
        }
    }
}

Enumerate using default iterator:
  A (AA)
  B (BB)
  C (CC)
Enumerate using the FirstTwo iterator:
  A (AA)
  B (BB)
Enumerate using the Reverse iterator:
  C (CC)
  B (BB)
  A (AA)

yield value for IEnumerable

using System;
using System.Collections.Generic;
public class MainClass
{
    static public IEnumerable<int> Powers( int from,
                                           int to ) {
        for( int i = from; i <= to; ++i ) {
            yield return (int) Math.Pow( 2, i );
        }
    }
    static void Main() {
        IEnumerable<int> powers = Powers( 0, 16 );
        foreach( int result in powers ) {
            Console.WriteLine( result );
        }
    }
}

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