org.javarosa.xform.parse

Class FisherYates

java.lang.Object

org.javarosa.xform.parse.FisherYates

public class FisherYates
extends Object

This class implements the Fisher-Yates list shuffling algorithm.

Combined with the ParkMiller Random Number Generator implementation on this library, cross-platform reproducible results can be guaranteed.

Verified compatible libraries are:

• Javascript - fisher-yates npm module
• Javascript - park-miller npm module

Using other libraries won't guarantee reproducible results.

The main difference between this implementation and the native Collections.shuffle(java.util.List<?>) consist on the way this one selects which elements to swap on each iteration. See inlined comments for more information.

Constructor Summary

Constructors

Constructor and Description
FisherYates()

Method Summary

Modifier and Type	Method and Description
static <T> List<T>	shuffle(List<T> input) Shuffle the input list of elements using a Random Random Number Generator instance to decide which positions get swapped on each iteration.
static <T> List<T>	shuffle(List<T> input, long seed) Shuffle the input list of elements using a ParkMiller Random Number Generator instance to decide which positions get swapped on each iteration.
static <T> List<T>	shuffle(List<T> input, Random random) Shuffle the input list of elements using a Random Random Number Generator instance to decide which positions get swapped on each iteration.

Methods inherited from class java.lang.Object

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

Constructor Detail

FisherYates

public FisherYates()

Method Detail

shuffle

public static <T> List<T> shuffle(List<T> input)

Shuffle the input list of elements using a Random Random Number Generator instance to decide which positions get swapped on each iteration.

Type Parameters:

T - Type parameter of the input List of elements

Parameters:

input - List of elements to be shuffled

Returns:

A new List of elements, containing the same elements as in the input List, but in a different order.

shuffle

public static <T> List<T> shuffle(List<T> input,
                                  long seed)

Shuffle the input list of elements using a ParkMiller Random Number Generator instance to decide which positions get swapped on each iteration.

Use the same seed for the RNGs when reproducible results are required.

Type Parameters:

T - Type parameter of the input List of elements

Parameters:

input - List of elements to be shuffled

seed - Long number to use as seed of the RNG

Returns:

A new List of elements, containing the same elements as in the input List, but in a different order.

shuffle

public static <T> List<T> shuffle(List<T> input,
                                  Random random)

Shuffle the input list of elements using a Random Random Number Generator instance to decide which positions get swapped on each iteration.

Use the same seed for the RNGs when reproducible results are required. Warning: It's recommended to use shuffle(List, long) instead, to ensure you are using a cross-platform RNG like ParkMiller.

Type Parameters:

T - Type parameter of the input List of elements

Parameters:

input - List of elements to be shuffled

random - Random instance with the RNG to be used

Returns:

A new List of elements, containing the same elements as in the input List, but in a different order.