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/*
* LingPipe v. 4.1.0
* Copyright (C) 2003-2011 Alias-i
*
* This program is licensed under the Alias-i Royalty Free License
* Version 1 WITHOUT ANY WARRANTY, without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Alias-i
* Royalty Free License Version 1 for more details.
*
* You should have received a copy of the Alias-i Royalty Free License
* Version 1 along with this program; if not, visit
* http://alias-i.com/lingpipe/licenses/lingpipe-license-1.txt or contact
* Alias-i, Inc. at 181 North 11th Street, Suite 401, Brooklyn, NY 11211,
* +1 (718) 290-9170.
*/
package com.aliasi.features;
import com.aliasi.util.AbstractExternalizable;
import com.aliasi.util.FeatureExtractor;
import java.io.IOException;
import java.io.NotSerializableException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
/**
* A {@code LengthNormFeatureExtractor} converts feature vectors
* produced by a contained extractor into unit length vectors.
*
* Length is defined as the (Euclidean or L2) distance from the
* origin, which is given by:
*
*
* length(map) = sqrt(&Sigma{v in map.values()} v * v)
*
* If the length is non-zero, a new map is created in which all values
* are divided by the length, so that the returned value has unit
* length (length = 1). If the length is zero, the feature vector
* extracted by the contained feature extractor is returned as is.
*
* Serialization
*
*
A length-norm feature
* extractor is serializable if its contained base extractor is
* serializable.
*
* @author Bob Carpenter
* @version 3.8
* @since Lingpipe3.8
* @param The type of object whose features are extracted
*/
public class LengthNormFeatureExtractor
extends FeatureExtractorFilter
implements Serializable {
static final long serialVersionUID = -5628628360712035433L;
/**
* Construct a length-normalized feature extractor from the
* specified extractor.
*
* @param extractor Base feature extractor.
*/
public LengthNormFeatureExtractor(FeatureExtractor extractor) {
super(extractor);
}
/**
* Return a length-normalized feature version of the
* feature vector returned by the contained vector.
*
* @return The length-normalized feature vector.
*/
@Override
public Map features(E in) {
Map baseMap = baseExtractor().features(in);
double sumOfSquares = 0.0;
for (Number n : baseMap.values()) {
double val = n.doubleValue();
sumOfSquares += val * val;
}
if (sumOfSquares == 0.0)
return baseMap;
double length = java.lang.Math.sqrt(sumOfSquares);
Map resultMap = new HashMap();
for (Map.Entry entry : baseMap.entrySet())
resultMap.put(entry.getKey(), entry.getValue().doubleValue()
/ length);
return resultMap;
}
Object writeReplace() {
return new Serializer(this);
}
static class Serializer extends AbstractExternalizable {
static final long serialVersionUID = 6365515337527915147L;
private final LengthNormFeatureExtractor mFilter;
public Serializer() {
this(null);
}
public Serializer(LengthNormFeatureExtractor filter) {
mFilter = filter;
}
@Override
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject(mFilter.mExtractor);
}
@Override
public Object read(ObjectInput in)
throws IOException, ClassNotFoundException {
@SuppressWarnings("unchecked")
// required for deserialization
FeatureExtractor extractor
= (FeatureExtractor) in.readObject();
return new LengthNormFeatureExtractor(extractor);
}
}
}