datafu.pig.hash.lsh

Class RepeatingLSH

java.lang.Object

datafu.pig.hash.lsh.interfaces.LSH

datafu.pig.hash.lsh.RepeatingLSH

public class RepeatingLSH
extends LSH

A composite hash which takes multiple hashes and composes them. This is useful when a locality sensitive hash has a range that is very narrow and would want a wider range for the hash.

Field Summary

Fields inherited from class datafu.pig.hash.lsh.interfaces.LSH

dim, rg

Constructor Summary

Constructors

Constructor and Description
RepeatingLSH(java.util.List<LSH> lshList)

Method Summary

Modifier and Type	Method and Description
long	apply(org.apache.commons.math.linear.RealVector vector) Compute the aggregated hash of a vector.

Methods inherited from class datafu.pig.hash.lsh.interfaces.LSH

getDim, getRandomGenerator

Methods inherited from class java.lang.Object

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

Constructor Detail

RepeatingLSH

public RepeatingLSH(java.util.List<LSH> lshList)
             throws org.apache.commons.math.MathException

Throws:

org.apache.commons.math.MathException

Method Detail

apply

public long apply(org.apache.commons.math.linear.RealVector vector)

Compute the aggregated hash of a vector. This is done by taking the output of the k hashes as a vector and computing the dot product with a vector of uniformly distributed components between 0 and 10. So, consider a_{0,k} such that a_i ~ U(0,10) and hash functions h_{0,k} treated as 2 k-dimensional vectors, we return the dot product of h(v) and a.

Specified by:

apply in class LSH

Parameters:

vector - A vector to be hashed

Returns:

A hash which collides with vectors close according to some metric (implementation dependent).