如何在 Lucene 中获取文档术语向量的文档 ID

Question

我是 Lucene 世界的新手，对该主题没有太多的工作知识。我需要提取文档术语向量，我在网上找到了以下代码How to extract Document Term Vector in Lucene 3.5.0。

 /**
 * Sums the term frequency vector of each document into a single term frequency map
 * @param indexReader the index reader, the document numbers are specific to this reader
 * @param docNumbers document numbers to retrieve frequency vectors from
 * @param fieldNames field names to retrieve frequency vectors from
 * @param stopWords terms to ignore
 * @return a map of each term to its frequency
 * @throws IOException
 */
private Map<String,Integer> getTermFrequencyMap(IndexReader indexReader, List<Integer> docNumbers, String[] fieldNames, Set<String> stopWords)
throws IOException {
    Map<String,Integer> totalTfv = new HashMap<String,Integer>(1024);

    for (Integer docNum : docNumbers) {
        for (String fieldName : fieldNames) {
            TermFreqVector tfv = indexReader.getTermFreqVector(docNum, fieldName);
            if (tfv == null) {
                // ignore empty fields
                continue;
            }

            String terms[] = tfv.getTerms();
            int termCount = terms.length;
            int freqs[] = tfv.getTermFrequencies();

            for (int t=0; t < termCount; t++) {
                String term = terms[t];
                int freq = freqs[t];

                // filter out single-letter words and stop words
                if (StringUtils.length(term) < 2 ||
                    stopWords.contains(term)) {
                    continue; // stop
                }

                Integer totalFreq = totalTfv.get(term);
                totalFreq = (totalFreq == null) ? freq : freq + totalFreq;
                totalTfv.put(term, totalFreq);
            }
        }
    }

    return totalTfv;
}

我已经创建了位于以下目录中的索引。

String indexDir = "C:\\Lucene\\Output\\";
Directory dir = FSDirectory.open(new File(indexDir));
IndexReader reader = IndexReader.open(dir);

我的问题是我不知道如何获取上述功能所需的文档 ID（列出文档编号）。我尝试了几种方法，例如

TermDocs docs = reader.termDocs();

但它不起作用。

Answer 1

Lucene 从零开始分配 id，maxDoc() 是上限，因此您可以简单地循环获取所有 id，跳过已删除的文档（Lucene 在调用 deleteDocument 时将它们标记为删除）：

for (int docNum=0; docNum < reader.maxDoc(); docNum++) {
    if (reader.isDeleted(docNum)) {
        continue;
    }
    TermFreqVector tfv = reader.getTermFreqVector(docNum, "fieldName");
    ...
}

为此，您必须在索引期间启用它们，请参阅Field.TermVector。