基于日期 20210419 的字符串排序列表

Question

I have. list of files, names of the files are log20211904.json what would be the best way to sort this name based on the date that is included in the name of the file? What I get now from my method substring is 20210419 which is not valid date time. I wonder how to do it effectively and get valid DateTimeOffset from 20210419

I was thinking

var orderedFIle = new List<LogFile>();
        
var fileDetail = new LogFile()
{
    FileName = "log20210419",

};
var fileDetailtest = new LogFile()
{
    FileName = "log20210420",

};
var test = fileDetail.FileName.Substring(3, 8);
Console.WriteLine(test);
orderedFIle.Add(fileDetail);
orderedFIle.Add(fileDetailtest);

var  list = orderedFIle.OrderByDescending(f => DateTime.Parse(f.FileName.Substring( 3,8)));
foreach (var VARIABLE in list)
{
    Console.WriteLine(VARIABLE.FileName);
}

But the date is actually without separators. What would be the best approach

Answer 1

Since the date in the string is already in a sortable format you can just sort by the full log name.

For example:

var l = new List<LogFile>();
l.Add(new LogFile(){FileName = "log20210419"});
l.Add(new LogFile(){FileName = "log20210420"});
l.Add(new LogFile(){FileName = "log20210101"});
foreach (var f in l.OrderByDescending(f => f.FileName))
{
    Console.WriteLine(f.FileName);
}

prints

log20210420
log20210419
log20210101

If you really want to parse then you can use ParseExact :

DateTime.ParseExact(f.FileName, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture)

Answer 2

Define a class as follows.

/// <summary>
/// Use a regular expression to validate the file name and extract the date parts.
/// Implement IComparable to define a default sort order.
/// </summary>
public class JsonLogFileName : IComparable<JsonLogFileName>
{
    // Private data members.
    private string fileName;
    private DateTime fileDate;

    // Public accessor methods.
    public String FileName => this.fileName;

    public DateTime FileDate => this.fileDate;

    /// <summary>
    /// Class constructor.
    /// </summary>
    /// <param name="fileName"></param>
    public JsonLogFileName(string fileName) {

        // Use a regular expression to validate the file name
        // and extract the date parts.
        Match m = Regex.Match(fileName, @"^log(\d{4})(\d{2})(\d{2}).json$");
        if (!m.Success) {
            throw new ArgumentException();
        }

        this.fileName = fileName;

        int year = int.Parse(m.Groups[1].Value);
        int month = int.Parse(m.Groups[2].Value);
        int day = int.Parse(m.Groups[3].Value);

        this.fileDate = new DateTime(year, month, day);
    }

    // Default sort order
    public int CompareTo(JsonLogFileName other) {
        return DateTime.Compare(this.FileDate, other.FileDate);
    }
}

You can use it like this.

public static void Main(String[] args) {

    List<JsonLogFileName> jsonLogFileNameList = new List<JsonLogFileName> {
        new JsonLogFileName("log20210419.json"),
        new JsonLogFileName("log20210418.json"),
        new JsonLogFileName("log20210417.json"),
        new JsonLogFileName("log20210416.json"),
        new JsonLogFileName("log20210415.json"),
    };

    jsonLogFileNameList.Sort();

    foreach (JsonLogFileName jsonFileName in jsonLogFileNameList) {
        Console.WriteLine($"{jsonFileName.FileName}: {jsonFileName.FileDate}");
    }

    Console.WriteLine("Press any key to continue.");
    Console.ReadKey();
}

Answer 3

Use IComparable

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace HotelManagement
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] filenames = {
                                     "log20211904.json",
                                     "log20211804.json",
                                     "log20211904.json",
                                     "log20210903.json",
                                     "log20211902.json",
                                     "log20211910.json",
                                     "log20211909.json"
                                 };

            string[] results = filenames.OrderBy(x => new SortFileName(x)).ToArray();

 
        }
    }
    public class SortFileName : IComparable<SortFileName>
    {
        private DateTime date { get; set; } 

        public SortFileName(string filename)
        {
            date = DateTime.ParseExact(filename.Substring(3,8), "yyyyddMM", System.Globalization.CultureInfo.InvariantCulture);
        }
        public int CompareTo(SortFileName other)
        {
            return this.date.CompareTo(other.date);

        }
    }
 
}