搜索引擎优化 TF_IDF之Java实现

实现之前，我们要事先说明一些问题：

我们用Redis对数据进行持久化，存两种形式的MAP:

key值为term，value值为含有该term的url
key值为url，value值为map，记录term及在文章中出现的次数
总的计算公式如下：

1.计算词频TF
这里通过给出url地址，获取搜索词term在此url中的数量，计算出TF

获取url中的词汇总数

/**
* @Author Ragty
* @Description 获取url中的词汇总数
* @Date 11:18 2019/6/4
**/
public Integer getWordCount(String url) {
String redisKey = urlSetKey(url);
Map<String,String> map = jedis.hgetAll(redisKey);
Integer count = 0;

for(Map.Entry<String, String> entry: map.entrySet()) {
count += Integer.valueOf(entry.getValue());
}
return count;
}
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返回搜索项在url中出现的次数

/**
* @Author Ragty
* @Description 返回搜索项在url中出现的次数
* @Date 22:12 2019/5/14
**/
public Integer getTermCount(String url,String term) {
String redisKey = urlSetKey(url);
String count = jedis.hget(redisKey,term);
return new Integer(count);
}
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获取搜索词的词频

/**
* @Author Ragty
* @Description 获取搜索词的词频(Term Frequency)
* @Date 11:25 2019/6/4
**/
public BigDecimal getTermFrequency(String url,String term) {
if (!isIndexed(url)) {
System.out.println("Doesn't indexed.");
return null;
}

Integer documentCount = getWordCount(url);
Integer termCount = getTermCount(url,term);
return documentCount==0 ? new BigDecimal(0) : new BigDecimal(termCount).divide(new BigDecimal(documentCount),6,BigDecimal.ROUND_HALF_UP);
}
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2.计算逆文档频率
计算逆文档频率，需要计算文档总数，以及包含该搜索词的文章数

获取redis索引文章的总数

/**
* @Author Ragty
* @Description 获取redis索引文章的总数
* @Date 19:46 2019/6/5
**/
public Integer getUrlCount() {
Integer count = 0;
count = urlSetKeys().size();
return count;
}
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获取含有搜索词的文章数

/**
* @Author Ragty
* @Description 获取含有搜索词的文章数
* @Date 22:42 2019/6/5
**/
public Integer getUrlTermCount(String term) {
Integer count = 0;
count = getUrls(term).size();
return count;
}
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计算逆文档频率IDF(InverseDocumnetFrequency)

/**
* @Author Ragty
* @Description 计算逆文档频率IDF(InverseDocumnetFrequency)
* @Date 23:32 2019/6/5
**/
public BigDecimal getInverseDocumentFrequency(String term) {
Integer totalUrl = getUrlCount();
Integer urlTermCount = getUrlTermCount(term);
Double xx = new BigDecimal(totalUrl).divide(new BigDecimal(urlTermCount),6,BigDecimal.ROUND_HALF_UP).doubleValue();
BigDecimal idf = new BigDecimal(Math.log10(xx));
return idf;
}
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3.获取TF-IDF
/**
* @Author Ragty
* @Description 获取tf-idf值
* @Date 23:34 2019/6/5
**/
public BigDecimal getTFIDF(String url,String term) {
BigDecimal tf = getTermFrequency(url, term);
BigDecimal idf = getInverseDocumentFrequency(term);
BigDecimal tfidf =tf.multiply(idf);
return tfidf;
}
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4.数据测试
这里我采用我自己爬取的部分数据，进行一下简单的测试(可能因为数据集的原因导致部分结果不准确)

测试类方法：

/**
* @Author Ragty
* @Description 获取tfidf下的相关性
* @Date 8:47 2019/6/6
**/
private static BigDecimal getRelevance(String url,String term,JedisIndex index) {
BigDecimal tfidf = index.getTFIDF(url,term);
return tfidf;
}


/**
* @Author Ragty
* @Description 执行搜索
* @Date 23:49 2019/5/30
**/
public static WikiSearch search(String term,JedisIndex index) {
Map<String,BigDecimal> map = new HashMap<String, BigDecimal>();
Set<String> urls = index.getUrls(term);

for (String url: urls) {
BigDecimal tfidf = getRelevance(url,term,index).setScale(6,BigDecimal.ROUND_HALF_UP);
map.put(url,tfidf);
}

return new WikiSearch(map);
}


/**
* @Author Ragty
* @Description 按搜索项频率顺序打印内容
* @Date 13:46 2019/5/30
**/
private void print() {
List<Entry<String,BigDecimal>> entries = sort();
for(Entry<String,BigDecimal> entry: entries) {
System.out.println(entry.getKey()+" "+entry.getValue());
}
}



/**
* @Author Ragty
* @Description 根据相关性对数据排序
* @Date 13:54 2019/5/30
**/
public List<Entry<String,BigDecimal>> sort(){
List<Entry<String,BigDecimal>> entries = new LinkedList<Entry<String, BigDecimal>>(map.entrySet());

Comparator<Entry<String,BigDecimal>> comparator = new Comparator<Entry<String, BigDecimal>>() {
@Override
public int compare(Entry<String, BigDecimal> o1, Entry<String, BigDecimal> o2) {
return o2.getValue().compareTo(o1.getValue());
}
};

Collections.sort(entries,comparator);
return entries;
}
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测试代码：

public static void main(String[] args) throws IOException {
Jedis jedis = JedisMaker.make();
JedisIndex index = new JedisIndex(jedis);

// search for the first term
String term1 = "java";
System.out.println("Query: " + term1);
WikiSearch search1 = search(term1, index);
search1.print();

// search for the second term
String term2 = "programming";
System.out.println("Query: " + term2);
WikiSearch search2 = search(term2, index);
search2.print();

}
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测试结果：

Query: java
https://baike.baidu.com/item/LiveScript 0.029956
https://baike.baidu.com/item/Java/85979 0.019986
https://baike.baidu.com/item/Brendan%20Eich 0.017188
https://baike.baidu.com/item/%E7%94%B2%E9%AA%A8%E6%96%87/471435 0.013163
https://baike.baidu.com/item/Sun/69463 0.005504
https://baike.baidu.com/item/Rhino 0.004401
https://baike.baidu.com/item/%E6%8E%92%E7%89%88%E5%BC%95%E6%93%8E 0.003452
https://baike.baidu.com/item/javascript 0.002212
https://baike.baidu.com/item/js/10687961 0.002212
https://baike.baidu.com/item/%E6%BA%90%E7%A0%81 0.002205
https://baike.baidu.com/item/%E6%BA%90%E7%A0%81/344212 0.002205
https://baike.baidu.com/item/%E8%84%9A%E6%9C%AC%E8%AF%AD%E8%A8%80 0.001989
https://baike.baidu.com/item/SQL 0.001779
https://baike.baidu.com/item/PHP/9337 0.001503
https://baike.baidu.com/item/iOS/45705 0.001499
https://baike.baidu.com/item/Netscape 0.000863
https://baike.baidu.com/item/%E6%93%8D%E4%BD%9C%E7%B3%BB%E7%BB%9F 0.000835
https://baike.baidu.com/item/Mac%20OS%20X 0.000521
https://baike.baidu.com/item/C%E8%AF%AD%E8%A8%80 0.000318

Query: programming
https://baike.baidu.com/item/C%E8%AF%AD%E8%A8%80 0.004854
https://baike.baidu.com/item/%E8%84%9A%E6%9C%AC%E8%AF%AD%E8%A8%80 0.002529
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