CSharp - GroupBy operator with part of the input element being processed with the elementSelector.

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Introduction

In the call to the GroupBy operator, elementSelector, the second argument, is returning the dateAwarded member.

Because we are returning a DateTime, our IGrouping is now for a type of DateTime, instead of StudentOptionEntry.

Demo

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
class Program/* www.j a va2s .  co  m*/
{
    static void Main(string[] args)
    {
        StudentOptionEntry[] empOptions = StudentOptionEntry.GetStudentOptionEntries();
        IEnumerable<IGrouping<int, DateTime>> opts = empOptions
          .GroupBy(o => o.id, e => e.dateAwarded);

        //  First enumerate through the sequence of IGroupings.
        foreach (IGrouping<int, DateTime> keyGroup in opts)
        {
            Console.WriteLine("Option records for Student: " + keyGroup.Key);

            //  Now enumerate through the grouping's sequence of DateTime elements.
            foreach (DateTime date in keyGroup)
                Console.WriteLine(date.ToShortDateString());
        }
    }
}
class StudentOptionEntry
{
    public int id;
    public long optionsCount;
    public DateTime dateAwarded;

    public static StudentOptionEntry[] GetStudentOptionEntries()
    {
        StudentOptionEntry[] empOptions = new StudentOptionEntry[] {
      new StudentOptionEntry {
        id = 1,
        optionsCount = 2,
        dateAwarded = DateTime.Parse("1990/12/31") },
      new StudentOptionEntry {
        id = 2,
        optionsCount = 3000,
        dateAwarded = DateTime.Parse("1992/06/30")  },
      new StudentOptionEntry {
        id = 2,
        optionsCount = 3000,
        dateAwarded = DateTime.Parse("1991/01/01")  },
      new StudentOptionEntry {
        id = 3,
        optionsCount = 5000,
        dateAwarded = DateTime.Parse("1997/09/30") },
      new StudentOptionEntry {
        id = 2,
        optionsCount = 3000,
        dateAwarded = DateTime.Parse("2000/04/01")  },
      new StudentOptionEntry {
        id = 3,
        optionsCount = 7500,
        dateAwarded = DateTime.Parse("1998/09/30") },
      new StudentOptionEntry {
        id = 3,
        optionsCount = 7500,
        dateAwarded = DateTime.Parse("1998/09/30") },
      new StudentOptionEntry {
        id = 4,
        optionsCount = 2456,
        dateAwarded = DateTime.Parse("1997/12/31") },
      new StudentOptionEntry {
        id = 101,
        optionsCount = 2,
        dateAwarded = DateTime.Parse("1998/12/31") }
    };

        return (empOptions);
    }
}

Result

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