org.apache.mahout.vectorizer.encoders

Class StaticWordValueEncoder

java.lang.Object

org.apache.mahout.vectorizer.encoders.FeatureVectorEncoder

org.apache.mahout.vectorizer.encoders.WordValueEncoder

org.apache.mahout.vectorizer.encoders.StaticWordValueEncoder

Direct Known Subclasses:

CachingStaticWordValueEncoder

public class StaticWordValueEncoder
extends WordValueEncoder

Encodes a categorical values with an unbounded vocabulary. Values are encoding by incrementing a few locations in the output vector with a weight that is either defaulted to 1 or that is looked up in a weight dictionary. By default, only one probe is used which should be fine but could cause a decrease in the speed of learning because more features will be non-zero. If a large feature vector is used so that the probability of feature collisions is suitably small, then this can be decreased to 1. If a very small feature vector is used, the number of probes should probably be increased to 3.

Field Summary

Fields inherited from class org.apache.mahout.vectorizer.encoders.FeatureVectorEncoder

CONTINUOUS_VALUE_HASH_SEED, WORD_LIKE_VALUE_HASH_SEED

Constructor Summary

Constructors

Constructor and Description
StaticWordValueEncoder(String name)

Method Summary

Methods

Modifier and Type	Method and Description
protected int	hashForProbe(byte[] originalForm, int dataSize, String name, int probe) Provides the unique hash for a particular probe.
void	setDictionary(Map<String,Double> dictionary) Sets the weighting dictionary to be used by this encoder.
void	setMissingValueWeight(double missingValueWeight) Sets the weight that is to be used for values that do not appear in the dictionary.
protected double	weight(byte[] originalForm)

Methods inherited from class org.apache.mahout.vectorizer.encoders.WordValueEncoder

addToVector, asString, getWeight

Methods inherited from class org.apache.mahout.vectorizer.encoders.FeatureVectorEncoder

addToVector, addToVector, addToVector, bytesForString, getName, getProbes, hash, hash, hash, hash, hash, hashesForProbe, isTraceEnabled, setProbes, setTraceDictionary, trace, trace

Methods inherited from class java.lang.Object

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

Constructor Detail

StaticWordValueEncoder

public StaticWordValueEncoder(String name)

Method Detail

hashForProbe

protected int hashForProbe(byte[] originalForm,
               int dataSize,
               String name,
               int probe)

Description copied from class: FeatureVectorEncoder

Provides the unique hash for a particular probe. For all encoders except text, this is all that is needed and the default implementation of hashesForProbe will do the right thing. For text and similar values, hashesForProbe should be over-ridden and this method should not be used.

Overrides:

hashForProbe in class WordValueEncoder

Parameters:

originalForm - The original byte array value

dataSize - The length of hte vector being encoded

name - The name of the variable being encoded

probe - The probe number

Returns:

The hash of the current probe

setDictionary

public void setDictionary(Map<String,Double> dictionary)

Sets the weighting dictionary to be used by this encoder. Also sets the missing value weight to be half the smallest weight in the dictionary.

Parameters:

dictionary - The dictionary to use to look up weights.

setMissingValueWeight

public void setMissingValueWeight(double missingValueWeight)

Sets the weight that is to be used for values that do not appear in the dictionary.

Parameters:

missingValueWeight - The default weight for missing values.

weight

protected double weight(byte[] originalForm)

Specified by:

weight in class WordValueEncoder