Best Practice to find best matching instance in a List C#

Question

For sure very simple question for most of you. But I am struggling with a solution at the moment.

Imagine you have a list of cats (List) where each cat has a list of babys (Kitten)

public class Cat
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public string Race { get; set; }
        public bool Gender { get; set; }
        public List<Kitten> Babys { get; set; }  
    }

public class Kitten
    {
        public string Name { get; set; }
        public double Age { get; set; }
        public bool Gender { get; set; }
    }

now I want to find the Cat that has the most matches for given requirements. It could easily be the case that a cat matches only 2 of 3 requirements. I simple want to find the cat that has the most matches to my requirements.

where my requirements could be:

• Name has to be "Micky"
• Age is 42
• Has a Kitten named "Mini"

My actual solution would be to compare all properties and take the one with the highest count of matching properties. But this is not generic and I am sure there are mutch better ways to do it.

Thanks in advance

Answer 1

While this is the most generic solution there is (need some edge case improvements):

  public class ReflectCmpare
    {
        public PropertyInfo PropertyInfo { get; set; }
        public dynamic Value { get; set; }
    }


    public Cat GetBestCat(List<Cat> listOfCats, List<ReflectCmpare> catParamsToCompare, List<ReflectCmpare> kittensParamsToCompare)
    {
        var bestScore = 0;
        var ret = listOfCats[0];
        foreach (var cat in listOfCats)
        {
            var score = catParamsToCompare.Sum(param => param.PropertyInfo.GetValue(cat, null) == param.Value ? 1 : 0);
            foreach (var baby in cat.Babys)
            {
                score+= kittensParamsToCompare.Sum(param => param.PropertyInfo.GetValue(baby, null) == param.Value ? 1 : 0);
            }

            if (score <= bestScore) continue;
            bestScore = score;
            ret = cat;
        }
        return ret;
    }

You should really think about just doing simple compare function considering this objects is not dynamic this is the way to go:

public Cat GetBestCat(List<Cat> listOfCats, string name , int? age , bool? gender, string race ,string babyName,int? babyAge,bool? babyGender )
    {
        var ret = listOfCats[0];
        var highestScore = 0;
        foreach (var cat in listOfCats)
        {
            var score = 0;
            score += name != null && cat.Name.Equals(name) ? 1 : 0;
            score += age.HasValue && cat.Age.Equals(age.Value) ? 1 : 0;
            score += gender.HasValue && cat.Gender.Equals(gender.Value) ? 1 : 0;
            score += race != null && cat.Race.Equals(race) ? 1 : 0;
            score += name != null && cat.Name.Equals(name) ? 1 : 0;
            score += cat.Babys
                .Where(k => babyName==null || k.Name.Equals(babyName))
                .Where(k => !babyAge.HasValue || k.Age.Equals(babyAge.Value))
                .Any(k => !babyGender.HasValue || k.Gender.Equals(babyGender.Value))?1:0;
            if (score <= highestScore) continue;
            highestScore = score;
            ret = cat;
        }

        return ret;
    }

Answer 2

So, I see that the problem is you don't know if in any near future you will have more properties, so I will suggest going to the hardway and make reflection, the following is ugly af but you can probably (you will) make it better and hopefully serves you well as guiadance:

public static List<Cat> CheckProperties(List<Cat> inCatList, Cat inQueryCat)
{
    Dictionary<Cat, List<PropertyInfo>> dict = new Dictionary<Cat, List<PropertyInfo>>();

    foreach (PropertyInfo pI in inQueryCat.GetType().GetProperties())
    {
        var value = pI.GetValue(inQueryCat);

        if (value != null)
        {
            var cats = inCatList.Where(cat => cat.GetType().GetProperty(pI.Name).GetValue(cat).Equals(value));

            foreach (Cat cat in cats)
            {
                if (dict.ContainsKey(cat))
                {
                    dict[cat].Add(pI);
                }
                else
                {
                    dict.Add(cat, new List<PropertyInfo>() {pI});
                }
            }
        }
    }

    int max = Int32.MinValue;
    foreach (KeyValuePair<Cat, List<PropertyInfo>> keyValuePair in dict)
    {
        if (keyValuePair.Value.Count > max)
        {
            max = keyValuePair.Value.Count;
        }
    }

    return dict.Where(pair => pair.Value.Count == max).Select(pair => pair.Key).ToList();
}

Answer 3

Well, I have no opportunity to test this solution, but you can try this:

Assume that you have a list of cats:

var cats = new List<Cat>();

Now you have defined what are your criteria:

var desiredName = "Micky";
var desiredAge = 42;
var desiredKitten = "Mini";

And then you have to get your desired cat:

var desiredCat = cats
        .Select(c => new {
            Rating = 
                Convert.ToInt32(c.Age == desiredAge) +       // Here you check first criteria
                Convert.ToInt32(c.Name == desiredName) +     // Check second
                Convert.ToInt32(c.Babys.Count(b => b.Name == desiredKitten) > 0),   // And the third one
            c })
        .OrderByDescending(obj => obj.Rating) // Here you order them by number of matching criteria
        .Select(obj => obj.c) // Then you select only cats from your custom object
        .First(); // And get the first of them

Please check if this works for you. And if you need more specific answer or some edits for me to add.

Answer 4

If you really will compare 2 ou 3 requirements you can simplify using Linq by:

// try to find with 3 requirements
var foundCats = catList.Where(t => t.Name == desiredName && 
                                   t.Age == desiredAge &&
                                   t.Babys.Any(k => k.Name == desiredKitten)
                             ).ToList();

if (foundCats.Any())
{
    // you found the desired cat (or cats)
    return foundCats;
}

// try to find with 2 requirements
foundCats = catList.Where(t => 
    (t.Name == desiredName && t.Age == desiredAge) ||
    (t.Name == desiredName && t.Babys.Any(k => k.Name == desiredKitten)) ||
    (t.Age == desiredAge && t.Babys.Any(k => k.Name == desiredKitten)
).ToList();

if (foundCats.Any())
{
    // you found the desired cat (or cats)
    return foundCats;
}

// try to find with only 1 requirement
foundCats = catList.Where(t => t.Name == desiredName || 
                               t.Age == desiredAge ||
                               t.Babys.Any(k => k.Name == desiredKitten)
                         ).ToList();
return foundCats;