Package squidpony.squidmath

Class WeightedTable

java.lang.Object
squidpony.squidmath.WeightedTable
All Implemented Interfaces:
Serializable
public class WeightedTable
extends Object
implements Serializable
A different approach to the same task ProbabilityTable solves, though this only looks up an appropriate index instead of also storing items it can choose; allows positive doubles for weights but does not allow nested tables for simplicity. This doesn't store an RNG (or RandomnessSource) in this class, and instead expects a long to be given for each random draw from the table (these long parameters can be random, sequential, or in some other way different every time). Uses Vose's Alias Method, and is based fairly-closely on the code given by Keith Schwarz at that link. Because Vose's Alias Method is remarkably fast (O(1) generation time in use, and O(n) time to construct a WeightedTable instance), this may be useful to consider if you don't need all the features of ProbabilityTable or if you want deeper control over the random aspects of it.
Internally, this uses DiverRNG's algorithm as found in DiverRNG.determineBounded(long, int) and DiverRNG.determine(long) to generate two ints, one used for probability and treated as a 31-bit integer and the other used to determine the chosen column, which is bounded to an arbitrary positive int. It does this with just one randomized 64-bit value, allowing the state given to random(long) to be just one long.
Created by Tommy Ettinger on 1/5/2018.
See Also:
Serialized Form

  • Field Summary

    Fields 
    Modifier and Type Field Description
    protected int[] mixed  
    int size  

  • Constructor Summary

    Constructors 
    Constructor Description
    WeightedTable()
    Constructs a useless WeightedTable that always returns the index 0.
    WeightedTable​(double... probabilities)
    Constructs a WeightedTable with the given array of weights for each index.

  • Method Summary

    Modifier and Type Method Description
    static WeightedTable deserializeFromString​(String data)  
    int random​(long state)
    Gets an index of one of the weights in this WeightedTable, with the choice determined deterministically by the given long, but higher weights will be returned by more possible inputs than lower weights.
    String serializeToString()  

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

  • Constructor Details

    • WeightedTable

      public WeightedTable()
      Constructs a useless WeightedTable that always returns the index 0.

    • WeightedTable

      public WeightedTable​(double... probabilities)
      Constructs a WeightedTable with the given array of weights for each index. The array can also be a varargs for convenience. The weights can be any positive non-zero doubles, but should usually not be so large or small that precision loss is risked. Each weight will be used to determine the likelihood of that weight's index being returned by random(long).
      Parameters:
      probabilities - an array or varargs of positive doubles representing the weights for their own indices

  • Method Details

    • random

      public int random​(long state)
      Gets an index of one of the weights in this WeightedTable, with the choice determined deterministically by the given long, but higher weights will be returned by more possible inputs than lower weights. The state parameter can be from a random source, but this will randomize it again anyway, so it is also fine to just give sequential longs. The important thing is that each state input this is given will produce the same result for this WeightedTable every time, so you should give different state values when you want random-seeming results. You may want to call this like weightedTable.random(++state), where state is a long, to ensure the inputs change. This will always return an int between 0 (inclusive) and size (exclusive).
      Parameters:
      state - a long that should be different every time; consider calling with ++state
      Returns:
      a random-seeming index from 0 to size - 1, determined by weights and the given state

    • serializeToString

      public String serializeToString()

    • deserializeFromString

      public static WeightedTable deserializeFromString​(String data)