datafu.pig.hash.lsh.metric

Class L1

java.lang.Object

org.apache.pig.EvalFunc<org.apache.pig.data.Tuple>

datafu.pig.hash.lsh.metric.MetricUDF

datafu.pig.hash.lsh.metric.L1

public class L1
extends MetricUDF

A UDF used to find a vector v in a bag such that for query point q, metric m and threshold t m(v,q) < t. In other words, find the first vector in the bag within a threshold distance away.

It returns one of the tuples of the bag of vectors using L1 distance, distance between two vectors. This is otherwise known as the manhattan distance, taxicab distance or city block distance.

See Also:

L1PStableHash for an example

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.pig.EvalFunc

org.apache.pig.EvalFunc.SchemaType

Field Summary

Fields inherited from class datafu.pig.hash.lsh.metric.MetricUDF

dim

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

Constructors

Constructor and Description
L1(java.lang.String sDim) Create a new L1 Metric UDF with a given dimension.

Method Summary

Modifier and Type	Method and Description
protected double	dist(org.apache.commons.math.linear.RealVector v1, org.apache.commons.math.linear.RealVector v2) The distance metric used.
static double	distance(org.apache.commons.math.linear.RealVector v1, org.apache.commons.math.linear.RealVector v2)

Methods inherited from class datafu.pig.hash.lsh.metric.MetricUDF

exec, outputSchema

Methods inherited from class org.apache.pig.EvalFunc

allowCompileTimeCalculation, finish, getArgToFuncMapping, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, progress, setInputSchema, setPigLogger, setReporter, setUDFContextSignature, warn

Methods inherited from class java.lang.Object

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

Constructor Detail

L1

public L1(java.lang.String sDim)

Create a new L1 Metric UDF with a given dimension.

Parameters:

sDim - dimension

Method Detail

distance

public static double distance(org.apache.commons.math.linear.RealVector v1,
                              org.apache.commons.math.linear.RealVector v2)

dist

protected double dist(org.apache.commons.math.linear.RealVector v1,
                      org.apache.commons.math.linear.RealVector v2)

Description copied from class: MetricUDF

The distance metric used. Given v1 and v2, compute the distance between those vectors.

Specified by:

dist in class MetricUDF

Parameters:

v1 - first vector

v2 - second vector

Returns:

the distance between v1 and v2