/// <summary>
/// Re/Builds internal CDL (Cummulative Distribution List)
/// Must be called after modifying (calling Add or Remove), or it will break.
/// Switches between linear or binary search, depending on which one will be faster.
/// Might generate some garbage (list resize) on first few builds.
/// </summary>
/// <param name="seed">You can specify seed for internal random gen or leave it alone</param>
/// <returns>Returns itself</returns>
public IRandomSelector <T> Build(Int32 seed = -1)
{
if (_items.Count == 0)
{
throw new Exception("Cannot build with no items.");
}
// clear list and then transfer weights
_cdl.Clear();
foreach (Double weight in _weights)
{
_cdl.Add(weight);
}
RandomMath.BuildCumulativeDistribution(_cdl);
// default behavior
// if seed wasn't specified (it is seed==-1), keep same seed - avoids garbage collection from making new random
if (seed != -1)
{
// input -2 if you want to randomize seed
if (seed == -2)
{
seed = _random.Next();
}
_random = RandomUtils.Create(seed);
}
// RandomMath.ListBreakpoint decides where to use Linear or Binary search, based on internal buffer size
// if CDL list is smaller than breakpoint, then pick linear search random selector, else pick binary search selector
if (_cdl.Count < RandomMath.ListBreakpoint)
{
_select = RandomMath.SelectIndexLinearSearch;
}
else
{
_select = RandomMath.SelectIndexBinarySearch;
}
return(this);
}
/// <summary>
/// Builds StaticRandomSelector & clears internal buffers. Must be called after you finish Add-ing items.
/// </summary>
/// <param name="seed">Seed for random selector. If you leave it -1, the internal random will generate one.</param>
/// <returns>Returns IRandomSelector, underlying objects are either StaticRandomSelectorLinear or StaticRandomSelectorBinary. Both are non-mutable.</returns>
public IRandomSelector <T> Build(Int32 seed = -1)
{
T[] items = _items.ToArray();
Double[] cda = _weights.ToArray();
_items.Clear();
_weights.Clear();
RandomMath.BuildCumulativeDistribution(cda);
if (seed == -1)
{
seed = _random.Next();
}
// RandomMath.ArrayBreakpoint decides where to use Linear or Binary search, based on internal buffer size
// if CDA array is smaller than breakpoint, then pick linear search random selector, else pick binary search selector
if (cda.Length < RandomMath.ArrayBreakpoint)
{
return(new StaticRandomSelectorLinear <T>(items, cda, seed));
}
return(new StaticRandomSelectorBinary <T>(items, cda, seed));
}
