How to create sorting logic with custom date strings

Question

I want to write a sorting logic to sort the below strings as output of a custom class:

Output Now: 3m_20,2m_20,1m_20,10d_20,5d_20,0d_20,0d_0,5d_0,10d_0,1m_0,2m_0,3m_0

Required Output: 0d_0,0d_20,5d_0,5d_20,10d_0,10d_20,1m_0,1m_20,2m_0,2m_20,3m_0,3m_20

I am finding it difficult to complex to sort in the above fashion. Please help how can I sort as required ?

I have tried to sort it with the IComparable on the basis of Id but its sorting on the basis of the first character.

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            DateDefinition d1 = new DateDefinition { Horizon = "0d",Days=20};
            DateDefinition d1_0 = new DateDefinition { Horizon = "0d",Days=0};
            DateDefinition d2 = new DateDefinition { Horizon = "5d",Days=20};
            DateDefinition d2_0 = new DateDefinition { Horizon = "5d",Days=0};
            DateDefinition d3 = new DateDefinition { Horizon = "10d",Days=20};
            DateDefinition d3_0 = new DateDefinition { Horizon = "10d",Days=0};
            DateDefinition d4 = new DateDefinition { Horizon = "1m",Days=20};
            DateDefinition d4_0 = new DateDefinition { Horizon = "1m",Days=0};
            DateDefinition d5 = new DateDefinition { Horizon = "2m",Days=20};
            DateDefinition d5_0 = new DateDefinition { Horizon = "2m",Days=0};
            DateDefinition d6 = new DateDefinition { Horizon = "3m",Days=20};
            DateDefinition d6_0 = new DateDefinition { Horizon = "3m",Days=0};
        
            var definitions = new List<DateDefinition> {d6,d5,d4,d3,d2,d1,d1_0,d2_0,d3_0,d4_0,d5_0,d6_0};
        
            definitions.Sort();
        
            foreach(var d in definitions)
            {
                Console.WriteLine(d.Id);
            } 
        }
    }

    public class DateDefinition : IComparable<DateDefinition>
    {
        public string Horizon { get; set; }
        public int Days { get; set; }
        public string Id
        {
            get { return Horizon + "_" + Days.ToString(); }
        }
        
        public int CompareTo(DateDefinition other)
        {
            if (ReferenceEquals(other, this)) return 0;
            if(ReferenceEquals(other,null)) return -1;
            return string.Compare(Id,other.Id, StringComparison.InvariantCultureIgnoreCase);
        }
    }    
}

Output to the above code:

0d_0 0d_20 10d_0 10d_20 1m_0 1m_20 2m_0 2m_20 3m_0 3m_20 5d_0 5d_20

Need the output like:

0d_0 0d_20 5d_0 5d_20 10d_0 10d_20 1m_0 1m_20 2m_0 2m_20 3m_0 3m_20

Important Note: Please note that d=days , m=months in the above context.

What does Horizon = "5d",Days=20 mean? 5d seems to imply 5 days, but then what does Days=20 mean? — Eric J.
– Eric J., Commented Oct 15, 2022 at 15:41

jefftrotman · Accepted Answer · 2019-07-13 04:58:14Z

2

Inside the CompareTo method, you are using a string.Compare so it's comparing the calculated Id properties of the two instances alphabetically. Alphabetically "10d_0" comes before "5d_0".

You want to do some kind of numerical comparison, but you will need something to translate Horizon values stated in months into values stated in days (or vice-versa) to do a valid comparison.

It seems a little awkward defining the Horizon property as a string because it seems to contain a number and units (d for days or m for months). You will either need to parse those out and convert to numbers, or re-define Horizon into a numeric HorizonValue and a string HorizonUnits.

answered Jul 13, 2019 at 4:58

jefftrotman

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1 Comment

hi_shobhit76 Over a year ago

Thanks jeff. Horizon property is a string as its a business requirement to denote it in such a way and do some further calclulations based on that.

Eric J. · Accepted Answer · 2022-10-15 15:53:11Z

You need CompareTo() to implement your custom business rule. As I understand it, your algorithm would be:

public int CompareTo(DateDefinition other)
{
    // I'm using the C# 8 range operator. Equivalent to Horizon.Length-1.
    var thisTimeUnit = Horizon[^1]; 
    var otherTimeUnit = other.Horizon[^1];
    
    // See if the time units are unequal. If there are more than 2 time units, you'll
    // want to associate a rank order with each and compare the rank orders.
    if (thisTimeUnit == 'm' && otherTimeUnit == 'd')
        return 1;
    else if (thisTimeUnit == 'd' && otherTimeUnit == 'm')
        return -1;

    // Sort by the numeric value of horizon if they are different
    var thisHorizon = int.Parse(Horizon[0..^1]);
    var otherHorizon = int.Parse(other.Horizon[0..^1]);
    
    if (thisHorizon != otherHorizon)
        return thisHorizon - otherHorizon;
    
    // If we get here, we have to sort by Days because Horizon is the same
    return Days - other.Days;
}

Olivier Jacot-Descombes · Accepted Answer · 2022-10-15 16:13:17Z

The class DateDefinition must implement IComparable<DateDefinition> for sorting to work as expected.

In the following example I add some logic to the Horizon property. The setter splits the passed string into a number and a unit and stores them in the fields char? _horizonUnit; int? _horizonNumber;;

The getter combines these parts to recreate the original string.

public class DateDefinition : IComparable<DateDefinition>
{
    private char? _horizonUnit;
    private int? _horizonNumber;

    public string Horizon
    {
        get => _horizonNumber.HasValue ? _horizonNumber.ToString() + _horizonUnit : null;
        set {
            if (String.IsNullOrEmpty(value)) {
                _horizonUnit = null;
                _horizonNumber = null;
            } else {
                _horizonUnit = value[^1];
                if (Int32.TryParse(value[..^1], out int i)) {
                    _horizonNumber = i;
                } else {
                    _horizonNumber = null;
                    _horizonUnit = null;
                    throw new ArgumentException("Horizon does not contain a valid number");
                }
            }
        }
    }

    public int Days { get; set; }

    public string Id => $"{Horizon}_{Days}";

    public override string ToString() => Id;

    public int CompareTo(DateDefinition? other)
    {
        if (other == null) {
            return 1;
        } else {
            int comp = (_horizonUnit ?? (char)0).CompareTo(other._horizonUnit ?? (char)0);
            if (comp != 0) {
                return comp;
            }
            comp = (_horizonNumber ?? 0).CompareTo(other._horizonNumber ?? 0);
            if (comp != 0) {
                return comp;
            }
            return Days.CompareTo(other.Days);
        }
    }
}

ComparesTo returns -1 if this is less than other, 0 if both are equal and +1 if this is greater then other.

First it compares the units. It happens that 'd' is less than 'm', so, the built-in Char.CompareTo returns the desired order. If the units are equal, we compare the horizon numbers. If those are equal as well we compare the Days.

Note that I have overridden ToString to let it return Id. So, you can simply write Console.WriteLine(d); now. This is also better for debugging, as the debugger now displays the Id for DateDefinition objects.

Note also that I have used the new Indexes and Ranges feature of C#. If you cannot use them, you can use String.Subtring instead (it's a bit more cumbersome).

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