/// <summary>
/// Selects a single item based in the weights
/// </summary>
/// <returns>The value of the item</returns>
public T Select()
{
if (_items.Count == 0)
{
throw new InvalidOperationException("There was no items to select from");
}
Build();
return(WeightedHelper <T> .SelectItem(_items, _cumulativeWeights, GenerateRandomWeight(_items)).Value);
}
/// <summary>
/// Selects multiple items based in the weights
/// </summary>
/// <param name="count">The number of items to select</param>
/// <returns>A list containing the values of the items selected</returns>
public IEnumerable <T> Select(int count)
{
if (count <= 0)
{
throw new InvalidOperationException("Count must be > 0.");
}
if (_items.Count == 0)
{
throw new InvalidOperationException("There were no items to select from.");
}
if (!_options.HasFlag(SelectorOptions.AllowDuplicates) && _items.Count < count)
{
throw new InvalidOperationException("There aren't enough items in the collection to take " + count);
}
Build();
if (_options.HasFlag(SelectorOptions.AllowDuplicates))
{
for (var i = 0; i < count; i++)
{
yield return(WeightedHelper <T>
.SelectItem(_items, _cumulativeWeights, GenerateRandomWeight(_items)).Value);
}
}
// The code bellow can perform under O(log(n)) even when removing items from the list
// A shallow copy of the lists containing the items and the cumulative weights, since we will be removing items of the list we want to conserve the original ones
var items = new List <WeightedItem <T> >(_items);
var weights = new List <int>(_cumulativeWeightsList);
for (var i = 0; i < count; i++)
{
int index = WeightedHelper <T> .SelectItemIndex(items, weights, GenerateRandomWeight(items));
if (items.Count > 0)
{
items.RemoveAt(index);
}
if (weights.Count > 0)
{
weights.RemoveAt(index);
}
yield return(items[index].Value);
}
}
/// <summary>
/// Calculates the cumulative weights if it's needed
/// </summary>
public void Build()
{
if (!_forceRecalculation)
{
return;
}
_forceRecalculation = false;
(_cumulativeWeights, _totalCumulativeWeight) =
WeightedHelper <T> .CalculateCumulativeWeights(_items, _integerFactor);
// If the selector don't allow duplicates then it have to create a copy of the weights in list form
if (!_options.HasFlag(SelectorOptions.AllowDuplicates))
{
_cumulativeWeightsList = _cumulativeWeights.ToList();
}
}
