org.beryx.streamplify.shuffler

Class ShufflerImpl

java.lang.Object

org.beryx.streamplify.shuffler.ShufflerImpl

public class ShufflerImpl
extends java.lang.Object

A helper class that implements the shuffling logic used by the default shufflers (DefaultLongShuffler and DefaultBigIntegerShuffler).
This implementation is able to shuffle indices from very large sets.
The algorithm used by this class requires a constant amount of memory and runs in O(B) time, where B is the number of bytes used by the BigInteger internal representation of the cardinality of the set of indices.
Although it decently scatters the indices, this class will not produce uniformly distributed values (unless the set of indexes has a cardinality <= 256 and the random number generator produces uniformly distributed values).

Constructor Summary

Constructors

Constructor and Description
ShufflerImpl(java.util.Random rnd)

Method Summary

Modifier and Type	Method and Description
int[]	getRandomPermutation(int length)
java.math.BigInteger	getShuffledIndex(java.math.BigInteger index, java.math.BigInteger count) Retrieves the BigInteger value corresponding to index in a permutation with count elements.
long	getShuffledIndex(long index, long count) Retrieves the long value corresponding to index in a permutation with count elements.
ShufflerImpl	withSeed(long seed)

Methods inherited from class java.lang.Object

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

Constructor Detail

ShufflerImpl

public ShufflerImpl(java.util.Random rnd)

Parameters:

rnd - the random number generator used by this instance.

Method Detail

withSeed

public ShufflerImpl withSeed(long seed)

Parameters:

seed - the seed of the random generator used by this instance

Returns:

this instance

getShuffledIndex

public long getShuffledIndex(long index,
                             long count)

Retrieves the long value corresponding to index in a permutation with count elements.

getShuffledIndex

public java.math.BigInteger getShuffledIndex(java.math.BigInteger index,
                                             java.math.BigInteger count)

Retrieves the BigInteger value corresponding to index in a permutation with count elements.

getRandomPermutation

public int[] getRandomPermutation(int length)

Returns:

a random permutation with the given length.