TF-IDF (term frequency–inverse document frequency)

關於TF-IDF的source code，它用Perl語言寫成。

http://infomotions.com/blog/tag/term-frequencyinverse-document-frequency-tfidf/

另一個是用C#寫的：

http://www.codeproject.com/KB/cs/tfidf.aspx

其它相關的參考資源：

1. Ranking text documents based on TF-IDF

2. tf-idf (term frequency–inverse document frequency)

3. Information Retrieval (這文章講解得很詳細)