C#: Getting maximum and minimum values of arbitrary properties of all items in a list

Question

I have a specialized list that holds items of type IThing:

public class ThingList : IList
{...}

public interface IThing
{
    Decimal         


        

Answer 1

Yes, you should use a delegate and anonymous methods.

For an example see here.

Basically you need to implement something similar to the Find method of Lists.

Here is a sample implementation

public class Thing
{
    public int theInt;
    public char theChar;
    public DateTime theDateTime;
    
    public Thing(int theInt, char theChar, DateTime theDateTime)
    {
        this.theInt = theInt;
        this.theChar = theChar;
        this.theDateTime = theDateTime;
    }
    
    public string Dump()
    {
        return string.Format("I: {0}, S: {1}, D: {2}", 
            theInt, theChar, theDateTime);
    }
}

public class ThingCollection: List
{
    public delegate Thing AggregateFunction(Thing Best, 
                        Thing Candidate);
    
    public Thing Aggregate(Thing Seed, AggregateFunction Func)
    {
        Thing res = Seed;
        foreach (Thing t in this) 
        {
            res = Func(res, t);
        }
        return res;
    }
}

class MainClass
{
    public static void Main(string[] args)
    {
        Thing a = new Thing(1,'z',DateTime.Now);
        Thing b = new Thing(2,'y',DateTime.Now.AddDays(1));
        Thing c = new Thing(3,'x',DateTime.Now.AddDays(-1));
        Thing d = new Thing(4,'w',DateTime.Now.AddDays(2));
        Thing e = new Thing(5,'v',DateTime.Now.AddDays(-2));
        
        ThingCollection tc = new ThingCollection();
        
        tc.AddRange(new Thing[]{a,b,c,d,e});
        
        Thing result;

        //Max by date
        result = tc.Aggregate(tc[0], 
            delegate (Thing Best, Thing Candidate) 
            { 
                return (Candidate.theDateTime.CompareTo(
                    Best.theDateTime) > 0) ? 
                    Candidate : 
                    Best;  
            }
        );
        Console.WriteLine("Max by date: {0}", result.Dump());
        
        //Min by char
        result = tc.Aggregate(tc[0], 
            delegate (Thing Best, Thing Candidate) 
            { 
                return (Candidate.theChar < Best.theChar) ? 
                    Candidate : 
                    Best; 
            }
        );
        Console.WriteLine("Min by char: {0}", result.Dump());               
    }
}

The results:

Max by date: I: 4, S: w, D: 10/3/2008 12:44:07 AM
Min by char: I: 5, S: v, D: 9/29/2008 12:44:07 AM