cn.hutool.core.text.Simhash Maven / Gradle / Ivy
package cn.hutool.core.text;
import cn.hutool.core.lang.hash.MurmurHash;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.locks.StampedLock;
/**
*
* Simhash是一种局部敏感hash，用于海量文本去重。
* 算法实现来自：https://github.com/xlturing/Simhash4J
*
*
*
* 局部敏感hash定义：假定两个字符串具有一定的相似性，在hash之后，仍然能保持这种相似性，就称之为局部敏感hash。
*
*
* @author Looly, litaoxiao
* @since 4.3.3
*/
public class Simhash {
private final int bitNum = 64;
/** 存储段数，默认按照4段进行simhash存储 */
private final int fracCount;
private final int fracBitNum;
/** 汉明距离的衡量标准，小于此距离标准表示相似 */
private final int hammingThresh;
/** 按照分段存储simhash，查找更快速 */
private final List>> storage;
private final StampedLock lock = new StampedLock();
/**
* 构造
*/
public Simhash() {
this(4, 3);
}
/**
* 构造
*
* @param fracCount 存储段数
* @param hammingThresh 汉明距离的衡量标准
*/
public Simhash(int fracCount, int hammingThresh) {
this.fracCount = fracCount;
this.fracBitNum = bitNum / fracCount;
this.hammingThresh = hammingThresh;
this.storage = new ArrayList<>(fracCount);
for (int i = 0; i < fracCount; i++) {
storage.add(new HashMap<>());
}
}
/**
* 指定文本计算simhash值
*
* @param segList 分词的词列表
* @return Hash值
*/
public long hash(Collection segList) {
final int bitNum = this.bitNum;
// 按照词语的hash值，计算simHashWeight(低位对齐)
final int[] weight = new int[bitNum];
long wordHash;
for (CharSequence seg : segList) {
wordHash = MurmurHash.hash64(seg);
for (int i = 0; i < bitNum; i++) {
if (((wordHash >> i) & 1) == 1)
weight[i] += 1;
else
weight[i] -= 1;
}
}
// 计算得到Simhash值
final StringBuilder sb = new StringBuilder();
for (int i = 0; i < bitNum; i++) {
sb.append((weight[i] > 0) ? 1 : 0);
}
return new BigInteger(sb.toString(), 2).longValue();
}
/**
* 判断文本是否与已存储的数据重复
*
* @param segList 文本分词后的结果
* @return 是否重复
*/
public boolean equals(Collection segList) {
long simhash = hash(segList);
final List fracList = splitSimhash(simhash);
final int hammingThresh = this.hammingThresh;
String frac;
Map> fracMap;
final long stamp = this.lock.readLock();
try {
for (int i = 0; i < fracCount; i++) {
frac = fracList.get(i);
fracMap = storage.get(i);
if (fracMap.containsKey(frac)) {
for (Long simhash2 : fracMap.get(frac)) {
// 当汉明距离小于标准时相似
if (hamming(simhash, simhash2) < hammingThresh) {
return true;
}
}
}
}
} finally {
this.lock.unlockRead(stamp);
}
return false;
}
/**
* 按照(frac, 《simhash, content》)索引进行存储
*
* @param simhash Simhash值
*/
public void store(Long simhash) {
final int fracCount = this.fracCount;
final List>> storage = this.storage;
final List lFrac = splitSimhash(simhash);
String frac;
Map> fracMap;
final long stamp = this.lock.writeLock();
try {
for (int i = 0; i < fracCount; i++) {
frac = lFrac.get(i);
fracMap = storage.get(i);
if (fracMap.containsKey(frac)) {
fracMap.get(frac).add(simhash);
} else {
final List ls = new ArrayList<>();
ls.add(simhash);
fracMap.put(frac, ls);
}
}
} finally {
this.lock.unlockWrite(stamp);
}
}
//------------------------------------------------------------------------------------------------------ Private method start
/**
* 计算汉明距离
*
* @param s1 值1
* @param s2 值2
* @return 汉明距离
*/
private int hamming(Long s1, Long s2) {
final int bitNum = this.bitNum;
int dis = 0;
for (int i = 0; i < bitNum; i++) {
if ((s1 >> i & 1) != (s2 >> i & 1))
dis++;
}
return dis;
}
/**
* 将simhash分成n段
*
* @param simhash Simhash值
* @return N段Simhash
*/
private List splitSimhash(Long simhash) {
final int bitNum = this.bitNum;
final int fracBitNum = this.fracBitNum;
final List ls = new ArrayList<>();
final StringBuilder sb = new StringBuilder();
for (int i = 0; i < bitNum; i++) {
sb.append(simhash >> i & 1);
if ((i + 1) % fracBitNum == 0) {
ls.add(sb.toString());
sb.setLength(0);
}
}
return ls;
}
//------------------------------------------------------------------------------------------------------ Private method end
}