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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.yacy.cora.document.analysis;
/*
* THIS CODE WAS COPIED FROM org.apache.solr.update.processor.TextProfileSignature
* - to get access to the 'newText' variable content which is otherwise lost in the process, used for debugging
* - to use the much faster Lookup3Signature instead of MD5Signature
*/
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.update.processor.Lookup3Signature;
/**
* <p>This implementation is copied from Apache Nutch. </p>
* <p>An implementation of a page signature. It calculates an MD5 hash
* of a plain text "profile" of a page.</p>
* <p>The algorithm to calculate a page "profile" takes the plain text version of
* a page and performs the following steps:
* <ul>
* <li>remove all characters except letters and digits, and bring all characters
* to lower case,</li>
* <li>split the text into tokens (all consecutive non-whitespace characters),</li>
* <li>discard tokens equal or shorter than MIN_TOKEN_LEN (default 2 characters),</li>
* <li>sort the list of tokens by decreasing frequency,</li>
* <li>round down the counts of tokens to the nearest multiple of QUANT
* (<code>QUANT = QUANT_RATE * maxFreq</code>, where <code>QUANT_RATE</code> is 0.01f
* by default, and <code>maxFreq</code> is the maximum token frequency). If
* <code>maxFreq</code> is higher than 1, then QUANT is always higher than 2 (which
* means that tokens with frequency 1 are always discarded).</li>
* <li>tokens, which frequency after quantization falls below QUANT, are discarded.</li>
* <li>create a list of tokens and their quantized frequency, separated by spaces,
* in the order of decreasing frequency.</li>
* </ul>
* This list is then submitted to an MD5 hash calculation.*/
public class EnhancedTextProfileSignature extends Lookup3Signature {
private float quantRate = 0.01f;
private int minTokenLen = 2;
private StringBuilder evalText = new StringBuilder(120); // start with some capacity, makes it much faster.
@Override
public void init(SolrParams params) {
quantRate = params.getFloat("quantRate", 0.01f);
minTokenLen = params.getInt("minTokenLen", 2);
}
@Override
public byte[] getSignature() {
return super.getSignature();
}
public StringBuilder getSignatureText() {
return evalText;
}
@Override
public void add(String content) {
HashMap<String, Token> tokens = new HashMap<String, Token>();
StringBuilder curToken = new StringBuilder();
int maxFreq = 0;
for (int i = 0; i < content.length(); i++) {
char c = content.charAt(i);
if (Character.isLetterOrDigit(c)) {
curToken.append(Character.toLowerCase(c));
} else {
if (curToken.length() > 0) {
if (curToken.length() > minTokenLen) {
// add it
String s = curToken.toString();
Token tok = tokens.get(s);
if (tok == null) {
tok = new Token(0, s);
tokens.put(s, tok);
}
tok.cnt++;
if (tok.cnt > maxFreq)
maxFreq = tok.cnt;
}
curToken.setLength(0);
}
}
}
// check the last token
if (curToken.length() > minTokenLen) {
// add it
String s = curToken.toString();
Token tok = tokens.get(s);
if (tok == null) {
tok = new Token(0, s);
tokens.put(s, tok);
}
tok.cnt++;
if (tok.cnt > maxFreq)
maxFreq = tok.cnt;
}
Iterator<Token> it = tokens.values().iterator();
ArrayList<Token> profile = new ArrayList<Token>();
// calculate the QUANT value
int quant = Math.round(maxFreq * quantRate);
if (quant < 2) {
if (maxFreq > 1)
quant = 2;
else
quant = 1;
}
while (it.hasNext()) {
Token t = it.next();
// round down to the nearest QUANT
t.qcnt = (t.cnt / quant) * quant;
// discard the frequencies below the QUANT
if (t.qcnt < quant) {
continue;
}
profile.add(t);
}
Collections.sort(profile, new TokenComparator());
StringBuilder newText = new StringBuilder(120);
it = profile.iterator();
while (it.hasNext()) {
Token t = it.next();
if (newText.length() > 0) {newText.append(' ');evalText.append(' ');}
newText.append('(').append(t.val).append('-').append(t.qcnt).append(')');
evalText.append('(').append(t.val).append('-').append(t.cnt).append('-').append(t.qcnt).append(')');
}
super.add(newText.toString());
}
private static class Token {
public int cnt, qcnt;
public String val;
public Token(int cnt, String val) {
this.cnt = cnt;
this.val = val;
}
@Override
public String toString() {
return val + " " + cnt;
}
}
private static class TokenComparator implements Comparator<Token> {
@Override
public int compare(Token t1, Token t2) {
return t2.cnt - t1.cnt;
}
}
public static long getSignatureLong(String text) {
Lookup3Signature sig = new Lookup3Signature();
sig.add(text);
return getSignatureLong(sig);
}
public static long getSignatureLong(String[] texts) {
Lookup3Signature sig = new Lookup3Signature();
for (String s: texts) sig.add(s);
return getSignatureLong(sig);
}
public static long getSignatureLong(Lookup3Signature sig) {
byte[] hash = sig.getSignature();
long l = 0;
for (int i = 0; i < 8; i++) l = (l << 8) + (hash[i] & 0xff);
return l;
}
}
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