/// <summary>
/// allows us to have zero-probability values
/// </summary>
private static int ExemptZeroes(Object[] objs, IRandomChoiceChooser chooser, int index)
{
//System.out.PrintLn(index);
if (chooser.GetProbability(objs[index]) == 0.0f)
// I need to scan forward because I'm in a left-trail
// scan forward
{
while (index < objs.Length - 1 && chooser.GetProbability(objs[index]) == 0.0f)
{
index++;
}
}
// scan backwards
else
{
while (index > 0 && chooser.GetProbability(objs[index]) == chooser.GetProbability(objs[index - 1]))
{
index--;
}
}
return(index);
}
/// <summary>
/// Picks a random item from an array of objects, each with an
/// associated probability that is accessed by taking an object
/// and passing it to chooser.GetProbability(obj). The objects'
/// probabilities are normalized and summed as follows:
/// For example, if four probabilities are {0.3, 0.2, 0.1, 0.4},
/// then they should get normalized and summed by the outside owners
/// as: {0.3, 0.5, 0.6, 1.0}. If probabilities.Length < checkboundary,
/// then a linear search is used, else a binary search is used.
/// </summary>
public static int PickFromDistribution(Object[] objs, IRandomChoiceChooser chooser, float prob, int checkboundary)
{
if (prob < 0.0f || prob > 1.0f)
{
throw new ArithmeticException("Invalid probability for PickFromDistribution (must be 0.0<=x<=1.0)");
}
if (objs.Length == 1)
{
return(0);
}
if (objs.Length < checkboundary)
{
// simple linear scan
for (var x = 0; x < objs.Length - 1; x++)
{
if (chooser.GetProbability(objs[x]) > prob)
{
return(ExemptZeroes(objs, chooser, x));
}
}
return(ExemptZeroes(objs, chooser, objs.Length - 1));
}
// binary search
var top = objs.Length - 1;
var bottom = 0;
while (top != bottom)
{
var cur = (top + bottom) / 2; // integer division
if (chooser.GetProbability(objs[cur]) > prob)
{
if (cur == 0 || chooser.GetProbability(objs[cur - 1]) <= prob)
{
return(ExemptZeroes(objs, chooser, cur));
}
// step down
else
{
top = cur;
}
}
else if (cur == objs.Length - 1)
{
// oops
return(ExemptZeroes(objs, chooser, cur));
}
else if (bottom == cur)
{
// step up
bottom++;
}
// (8 + 9)/2 = 8
else
{
bottom = cur; // (8 + 10) / 2 = 9
}
}
return(ExemptZeroes(objs, chooser, bottom)); // oops
}
/// <summary>
/// Normalizes the probabilities associated with an array of objects,
/// then converts them into continuing sums.
/// This prepares them for being usable in pickFromDistribution.
/// If the probabilities are all 0, then selection is uniform,
/// unless allowAllZeros is false, in which case an ArithmeticException is thrown.
/// If any of them are negative, or if the distribution is empty,
/// then an ArithmeticException is thrown.
/// For example,
/// {0.6, 0.4, 0.2, 0.8} -> {0.3, 0.2, 0.1, 0.4} -> {0.3, 0.5, 0.6, 1.0}
/// The probabilities are retrieved and set using chooser.
/// </summary>
public static void OrganizeDistribution(Object[] objs, IRandomChoiceChooser chooser, bool allowAllZeros)
{
// first normalize
var sum = 0.0;
if (objs.Length == 0)
{
throw new ArithmeticException("Distribution has no elements");
}
foreach (var t in objs)
{
if (chooser.GetProbability(t) < 0.0)
{
throw new ArithmeticException("Distribution has negative probabilities");
}
sum += chooser.GetProbability(t);
}
if (sum == 0.0)
{
if (!allowAllZeros)
{
throw new ArithmeticException("Distribution has all zero probabilities");
}
else
{
foreach (var t in objs)
{
chooser.SetProbability(t, 1.0f);
}
sum = objs.Length;
}
}
foreach (var t in objs)
{
//UPGRADE_WARNING: Data types in Visual C# might be different. Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
chooser.SetProbability(t, (float)(chooser.GetProbability(t) / sum));
}
// now sum
sum = 0.0;
foreach (var t in objs)
{
sum += chooser.GetProbability(t);
//UPGRADE_WARNING: Data types in Visual C# might be different. Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
chooser.SetProbability(t, (float)sum);
}
// now we need to work backwards setting 0 values
int x2;
for (x2 = objs.Length - 1; x2 > 0; x2--)
{
if (chooser.GetProbability(objs[x2]) == chooser.GetProbability(objs[x2 - 1]))
{
// we're 0.0
chooser.SetProbability(objs[x2], 1.0f);
}
else
{
break;
}
}
chooser.SetProbability(objs[x2], 1.0f);
}