Sort List, DateTimes

In a C# program, a List of DateTimes can be sorted. We can base this on the year or the month—any valid ordering of the times is possible.

It is sometimes necessary to sort DateTimes from most recent to least recent, and the opposite. Sorting based on the month is also useful.

Example code

This program creates a List of 4 DateTime values. Next it calls the 4 Sort custom methods. After the sorting is done we print out the lists with Console.WriteLine.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var list = new List<DateTime>();
        list.Add(new DateTime(1980, 5, 5));
        list.Add(new DateTime(1982, 10, 20));
        list.Add(new DateTime(1984, 1, 4));
        list.Add(new DateTime(1979, 6, 19));

        Display(SortAscending(list), "SortAscending");
        Display(SortDescending(list), "SortDescending");
        Display(SortMonthAscending(list), "SortMonthAscending");
        Display(SortMonthDescending(list), "SortMonthDescending");

    }

    static List<DateTime> SortAscending(List<DateTime> list)
    {
        list.Sort((a, b) => a.CompareTo(b));
        return list;
    }

    static List<DateTime> SortDescending(List<DateTime> list)
    {
        list.Sort((a, b) => b.CompareTo(a));
        return list;
    }

    static List<DateTime> SortMonthAscending(List<DateTime> list)
    {
        list.Sort((a, b) => a.Month.CompareTo(b.Month));
        return list;
    }

    static List<DateTime> SortMonthDescending(List<DateTime> list)
    {
        list.Sort((a, b) => b.Month.CompareTo(a.Month));
        return list;
    }

    static void Display(List<DateTime> list, string message)
    {
        Console.WriteLine(message);
        foreach (var datetime in list)
        {
            Console.WriteLine(datetime);
        }
        Console.WriteLine();
    }
}
SortAscending
6/19/1979 12:00:00 AM
5/5/1980 12:00:00 AM
10/20/1982 12:00:00 AM
1/4/1984 12:00:00 AM

SortDescending
1/4/1984 12:00:00 AM
10/20/1982 12:00:00 AM
5/5/1980 12:00:00 AM
6/19/1979 12:00:00 AM

SortMonthAscending
1/4/1984 12:00:00 AM
5/5/1980 12:00:00 AM
6/19/1979 12:00:00 AM
10/20/1982 12:00:00 AM

SortMonthDescending
10/20/1982 12:00:00 AM
6/19/1979 12:00:00 AM
5/5/1980 12:00:00 AM
1/4/1984 12:00:00 AM

The Ascending methods order the data from low to high, and the Descending methods do the opposite. Also, the SortMonth methods sort based on the month value of the DateTimes.

We looked at a way you can sort a List of DateTime instances in your C# program. It is also possible to sort with a query expression. This syntax might be clearer for some programmers.