Returned random item (weighted) from generic item factory

Question

I've got a problem with my item factory class for a little game I am trying to code at the moment. What I am doing at the moment is the following:

I've got a List containing all my possible game items of type x (armor, weapon, ...) with base class type Item
Each item has a rarity from the rarity enum (0 = common, 1 = uncommen, and so on)
The actual rarity "spawn" percentage is saved in a dictionary containing the rarity and the percentage
Currently I have a generic method returning new instances of random items:

public IEnumerable<T> GetRandomItem<T>(int count = 1, Rarity maxRarity = Rarity.Common, List<int> ids = null)
  where T : Item
{
  InitializeActualRarities(maxRarity);
  return GetItems<T>().ToList().Where(i => CheckItemConditions(ref i, maxRarity, ids)).Clone().PickRandom(count);
}

The item(s) returned by the GetRandomItem Method is(are) always a copy of (a) randomly picked object(s) from the item list.
The InitializeActualRarities method generates percentages for all rarities below max rarity:

    private void InitializeActualRarities(Rarity maxRarity)
    {
      _actualRarityPercentages.Clear();

      var remaining = 100;
      Enum.GetValues(typeof(Rarity)).OfType<Rarity>().Where(r => _staticRarityPercentages[r] >= _staticRarityPercentages[maxRarity]).ToList().ForEach(r =>
      {
        remaining -= _staticRarityPercentages[r];
        _actualRarityPercentages.Add(r, _staticRarityPercentages[r]);
      });

      var key = _actualRarityPercentages.Aggregate((l, r) => l.Value > r.Value ? l : r).Key;
      _actualRarityPercentages[key] += remaining;
    }

At the moment I am obviously not using the actual rarity percentage in my GetRandomItem Method, and that is just what I want to change.

I want adjust the linq in a way to ensure only items to the given max rarity are returned with the rarity percentages from the _actualRarityPercentages dictionary.

Has anybody an idea or some advice on how to solve that kind of task in my coding manner?

Thank you in advance!

score 1 · Answer 1 · answered Jul 18 '19 at 15:20

Something like this might work:

// Assuming this is the type
Dictionary<Rarity, int> _actualRarityPercentages;

public IEnumerable<T> GetRandomItem<T>(int count = 1, Rarity maxRarity = Rarity.Common, List<int> ids = null)
  where T : Item
{
  InitializeActualRarities(maxRarity);

  int maxRarityValue = _actualRarityPercentages[maxRarity];

  return GetItems<T>().ToList()
        .Where(item => _actualRarityPercentages[item.Rarity] <= maxRarityValue)
        .Clone()
        .PickRandom(count)
}

I've assumed that _actualRarityPercentages is a straightforward dictionary from Rarity to int. Using LINQ Where you should be able to filter the items that are more rare than maxRarity.

Hope that helps

That would work to ensure teh right rarity to be returned. This is actually already the case because I'm doing this check in the CheckItemCondition Call. What I need is just the weighted selection instead of just the selection. — epanalepsis, Jul 18 '19 at 15:28

score -1 · Answer 2 · answered Jul 18 '19 at 16:04

Try following :

public IEnumerable<T> GetRandomItem<T>(int count = 1, Rarity maxRarity = Rarity.Common, List<int> ids = null)
  where T : Item
{
  InitializeActualRarities(maxRarity);
  Random rand = new Rand();
  return GetItems<T>().ToList().Where(i => CheckItemConditions(ref i, maxRarity, ids)).Clone().Select((x,i) => new {item = x, rand = rand.Next()}).OrderBy(x => x.rand).Select(x => x.item).Take(count);
}

Returned random item (weighted) from generic item factory

2 Answers2