将文档的分词结果转化为非严格的UCI格式，即没有前三行的统计信息，因为这三行在LightLDA中没有使用到。
分词后结果的格式
doc1seqword1 word2 word3...
doc2seqword2 word3...
doc3seqword2 word3
seq是自定义的分割符，分割文档名和文档内容的分词结果，作为参数传入函数

/**
 * 将文本文件转化为UCI模式
 * @param seq  文档与分词结果的分隔符
 * @param filePath input 文本路径
 * @param docwordPath  output 转化后的文档信息存放路径
 * @param vocabPath    output 转化后的词汇信息存放路径
 * @throws Exception
 */
public static void text2UCI(String seq, String filePath, String docwordPath, String vocabPath) throws Exception{
    //先将分词结果中的各个词打乱赋予id存放到单词表中
    //再对文档进行处理
    //文档需要根据文档id排序，wordid从1开始
    //单词不能有空格或tab
    BufferedReader br = new BufferedReader(new FileReader(filePath));
    BufferedWriter vocab_bw = new BufferedWriter(new FileWriter(vocabPath));
    BufferedWriter doc_bw = new BufferedWriter(new FileWriter(docwordPath));

    HashSet<String> vocabs = new HashSet<>();

    String doc = null;
    while((doc = br.readLine()) != null){
        doc = doc.split(seq)[1];
        doc = doc.trim();
        if(doc.length() == 0){
            continue;
        }
        String[] words = doc.split(" +");  //按空格分组
        for(String word : words){
            vocabs.add(word);
        }
    }
    br.close();

    List<String> vocab_list = new ArrayList<>(vocabs);
    HashMap<String, Integer> vocab_id = new HashMap<>();
    int id = 1;
    for(String token : vocab_list){
        vocab_id.put(token, id++);
        vocab_bw.write(token);
        vocab_bw.newLine();
        vocab_bw.flush();  //写入到词汇表文件
    }
    vocab_bw.close();

    //防止文件过大，就不用mark和reset了
    br = new BufferedReader(new FileReader(filePath));
    int doc_id = 1;  //从1开始
    while((doc = br.readLine()) != null){
        doc = doc.split(seq)[1];
        doc = doc.trim();
        if(doc.length() == 0) continue;

        String[] words = doc.split(" +");  //按空格分组
        int[] ids = new int[words.length];
        for(int i = 0; i < words.length; ++i){
            ids[i] = vocab_id.get(words[i]);  //存放id
        }
        Arrays.sort(ids);
        HashMap<Integer, Integer> id_cnt = new HashMap<>();
        for(int word_id : ids){
            int value = id_cnt.containsKey(word_id) ? id_cnt.get(word_id) + 1 : 1;
            id_cnt.put(word_id, value);     //更新值
        }
        StringBuilder doc_info = new StringBuilder();
        doc_info.append(doc_id).append(" ").append(ids[0]).append(" ").append(id_cnt.get(ids[0])).append("\n");
        for(int i = 1; i < ids.length; ++i){
            if(ids[i] == ids[i-1]){
                continue;
            }
            doc_info.append(doc_id).append(" ").append(ids[i]).append(" ").append(id_cnt.get(ids[i])).append("\n");
        }
        doc_bw.write(doc_info.toString());
        doc_bw.flush();
        doc_id++;
    }
    br.close();
    doc_bw.close();

    System.out.println("vocab size : " + vocab_list.size());
    System.out.println("doc size: " + (doc_id - 1));
}