Class ListSampler

java.lang.Object
org.apache.commons.rng.sampling.ListSampler
public final class ListSampler extends Object
Sampling from a List.

This class also contains utilities for shuffling a List in-place.

Since:
1.0

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private static final int
    RANDOM_ACCESS_SIZE_THRESHOLD
    The size threshold for using the random access algorithm when the list does not implement java.util.RandomAccess.

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    private
    ListSampler()
    Class contains only static methods.

  • Method Summary

    Modifier and Type
    Method
    Description
    static <T> List<T>
    sample(UniformRandomProvider rng, List<T> collection, int k)
    Generates a list of size k whose entries are selected randomly, without repetition, from the items in the given collection.
    static <T> void
    shuffle(UniformRandomProvider rng, List<T> list)
    Shuffles the entries of the given array, using the Fisher-Yates algorithm.
    static <T> void
    shuffle(UniformRandomProvider rng, List<T> list, int start, boolean towardHead)
    Shuffles the entries of the given array, using the Fisher-Yates algorithm.
    private static void
    swap(Object[] array, int i, int j)
    Swaps the two specified elements in the array.
    private static <T> void
    swap(List<T> list, int i, int j)
    Swaps the two specified elements in the list.

    Methods inherited from class Object

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

  • Field Details

    • RANDOM_ACCESS_SIZE_THRESHOLD

      private static final int RANDOM_ACCESS_SIZE_THRESHOLD
      The size threshold for using the random access algorithm when the list does not implement java.util.RandomAccess.
      See Also:

  • Constructor Details

    • ListSampler

      private ListSampler()
      Class contains only static methods.

  • Method Details

    • sample

      public static <T> List<T> sample(UniformRandomProvider rng, List<T> collection, int k)
      Generates a list of size k whose entries are selected randomly, without repetition, from the items in the given collection.

      Sampling is without replacement; but if the source collection contains identical objects, the sample may include repeats.

      Sampling uses UniformRandomProvider.nextInt(int).

      Type Parameters:
      T - Type of the list items.
      Parameters:
      rng - Generator of uniformly distributed random numbers.
      collection - List to be sampled from.
      k - Size of the returned sample.
      Returns:
      a shuffled sample from the source collection.
      Throws:
      IllegalArgumentException - if k <= 0 or k > collection.size().

    • shuffle

      public static <T> void shuffle(UniformRandomProvider rng, List<T> list)
      Shuffles the entries of the given array, using the Fisher-Yates algorithm.

      Sampling uses UniformRandomProvider.nextInt(int).

      Type Parameters:
      T - Type of the list items.
      Parameters:
      rng - Random number generator.
      list - List whose entries will be shuffled (in-place).

    • shuffle

      public static <T> void shuffle(UniformRandomProvider rng, List<T> list, int start, boolean towardHead)
      Shuffles the entries of the given array, using the Fisher-Yates algorithm.

      The start and pos parameters select which part of the array is randomized and which is left untouched.

      Sampling uses UniformRandomProvider.nextInt(int).

      Type Parameters:
      T - Type of the list items.
      Parameters:
      rng - Random number generator.
      list - List whose entries will be shuffled (in-place).
      start - Index at which shuffling begins.
      towardHead - Shuffling is performed for index positions between start and either the end (if false) or the beginning (if true) of the array.

    • swap

      private static <T> void swap(List<T> list, int i, int j)
      Swaps the two specified elements in the list.
      Type Parameters:
      T - Type of the list items.
      Parameters:
      list - List.
      i - First index.
      j - Second index.

    • swap

      private static void swap(Object[] array, int i, int j)
      Swaps the two specified elements in the array.
      Parameters:
      array - Array.
      i - First index.
      j - Second index.