Alex
105 lines
3.3 KiB
C#
105 lines
3.3 KiB
C#
using SptCommon.Annotations;
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using Core.Models.Spt.Helper;
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using Core.Models.Utils;
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namespace Core.Helpers;
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[Injectable]
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public class WeightedRandomHelper(
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ISptLogger<WeightedRandomHelper> _logger
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)
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{
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/// <summary>
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/// Choose an item from the passed in array based on the weightings of each
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/// </summary>
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/// <param name="values">Items and weights to use</param>
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/// <returns>Chosen item from array</returns>
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public T GetWeightedValue<T>(Dictionary<T, double> values) where T : notnull
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{
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var itemKeys = values.Keys.ToList();
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var weights = values.Values.ToList();
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var chosenItem = WeightedRandom<T>(itemKeys, weights);
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return chosenItem.Item;
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}
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/// <summary>
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/// Picks the random item based on its weight.
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/// The items with higher weight will be picked more often (with a higher probability).
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///
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/// For example:
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/// - items = ['banana', 'orange', 'apple']
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/// - weights = [0, 0.2, 0.8]
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/// - weightedRandom(items, weights) in 80% of cases will return 'apple', in 20% of cases will return
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/// 'orange' and it will never return 'banana' (because probability of picking the banana is 0%)
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///
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/// </summary>
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/// <param name="items">List of items</param>
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/// <param name="weights">List of weights</param>
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/// <returns>Dictionary with item and index</returns>
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public WeightedRandomResult<T> WeightedRandom<T>(List<T> items, List<double> weights)
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{
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if (items.Count == 0)
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{
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_logger.Error("Items must not be empty");
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}
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if (weights.Count == 0)
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{
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_logger.Error("Item weights must not be empty");
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}
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if (items.Count != weights.Count)
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{
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_logger.Error("Items and weight inputs must be of the same length");
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}
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// Preparing the cumulative weights list.
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List<int> cumulativeWeights = [];
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for (var i = 0; i < weights.Count; i++)
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{
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cumulativeWeights.Add((int)(weights[i]) + (i > 0 ? (cumulativeWeights[i - 1]) : 0));
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}
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// Getting the random number in a range of [0...sum(weights)]
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int maxCumulativeWeight = cumulativeWeights[cumulativeWeights.Count - 1];
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double randomNumber = maxCumulativeWeight * new Random().NextDouble();
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// Picking the random item based on its weight.
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for (int itemIndex = 0; itemIndex < items.Count; itemIndex++)
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{
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if (cumulativeWeights[itemIndex] >= randomNumber)
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{
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return new WeightedRandomResult<T>()
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{
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Item = items[itemIndex],
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Index = itemIndex,
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};
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}
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}
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throw new InvalidOperationException("No item was picked.");
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}
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/// <summary>
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/// Find the greated common divisor of all weights and use it on the passed in dictionary
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/// </summary>
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/// <param name="weightedDict">Values to reduce</param>
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public void ReduceWeightValues(Dictionary<string, double> weightedDict)
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{
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throw new NotImplementedException();
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}
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protected double CommonDivisor(List<double> numbers)
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{
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throw new NotImplementedException();
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}
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protected double Gcd(double a, double b)
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{
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throw new NotImplementedException();
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}
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}
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