cern.jet.random.sampling
Class RandomSamplingAssistant

java.lang.Object
  |
  +--cern.colt.PersistentObject
        |
        +--cern.jet.random.sampling.RandomSamplingAssistant

All Implemented Interfaces:

java.lang.Cloneable, java.io.Serializable

public class RandomSamplingAssistant

extends PersistentObject

Conveniently computes a stable Simple Random Sample Without Replacement (SRSWOR) subsequence of n elements from a given input sequence of N elements; Example: Computing a sublist of n=3 random elements from a list (1,...,50) may yield the sublist (7,13,47). The subsequence is guaranteed to be stable, i.e. elements never change position relative to each other. Each element from the N elements has the same probability to be included in the n chosen elements. This class is a convenience adapter for RandomSampler using blocks.

See Also:

RandomSampler, Serialized Form

Field Summary

protected long[]	buffer
protected int	bufferPosition
protected long	n
protected RandomSampler	sampler
protected long	skip

Constructor Summary

RandomSamplingAssistant(long n, long N, RandomElement randomGenerator)
Constructs a random sampler that samples n random elements from an input sequence of N elements.

Method Summary

java.lang.Object	clone() Returns a deep copy of the receiver.
protected void	fetchNextBlock() Not yet commented.
RandomElement	getRandomGenerator() Returns the used random generator.
static void	main(java.lang.String[] args) Tests random sampling.
static int[]	sampleArray(int n, int[] elements) Just shows how this class can be used; samples n elements from and int[] array.
boolean	sampleNextElement() Returns whether the next element of the input sequence shall be sampled (picked) or not.
static void	test(long n, long N) Tests the methods of this class.
static void	testArraySampling(int n, int N) Tests the methods of this class.

Methods inherited from class java.lang.Object

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

Field Detail

sampler

protected RandomSampler sampler

buffer

protected long[] buffer

bufferPosition

protected int bufferPosition

skip

protected long skip

n

protected long n

Constructor Detail

RandomSamplingAssistant

public RandomSamplingAssistant(long n,
                               long N,
                               RandomElement randomGenerator)

Constructs a random sampler that samples n random elements from an input sequence of N elements.

Parameters:

n - the total number of elements to choose (must be >= 0).

N - number of elements to choose from (must be >= n).

randomGenerator - a random number generator. Set this parameter to null to use the default random number generator.

Method Detail

clone

public java.lang.Object clone()

Returns a deep copy of the receiver.

Overrides:

clone in class PersistentObject

Returns:

a copy of the receiver.

fetchNextBlock

protected void fetchNextBlock()

Not yet commented.

getRandomGenerator

public RandomElement getRandomGenerator()

Returns the used random generator.

main

public static void main(java.lang.String[] args)

Tests random sampling.

sampleArray

public static int[] sampleArray(int n,
                                int[] elements)

Just shows how this class can be used; samples n elements from and int[] array.

sampleNextElement

public boolean sampleNextElement()

Returns whether the next element of the input sequence shall be sampled (picked) or not.

Returns:

true if the next element shall be sampled (picked), false otherwise.

test

public static void test(long n,
                        long N)

Tests the methods of this class. To do benchmarking, comment the lines printing stuff to the console.

testArraySampling

public static void testArraySampling(int n,
                                     int N)

Tests the methods of this class. To do benchmarking, comment the lines printing stuff to the console.