文档的词频-反向文档频率(TF-IDF)计算

  private static Pattern r = Pattern.compile("([ \\t{}()\",:;. \n])"); 
  private static List<String> documentCollection;
 
    //Calculates TF-IDF weight for each term t in document d
    private static float findTFIDF(String document, String term)
    {
        float tf = findTermFrequency(document, term);
        float idf = findInverseDocumentFrequency(term);
        return tf * idf;
    }
 
    private static float findTermFrequency(String document, String term)
    {
      int count = getFrequencyInOneDoc(document, term);
 
        return (float)((float)count / (float)(r.split(document).length));
    }
    
    private static int getFrequencyInOneDoc(String document, String term)
    {
      int count = 0;
        for(String s : r.split(document))
        {
          if(s.toUpperCase().equals(term.toUpperCase())) {
            count++;
          }
        }
        return count;
    }
 
 
    private static float findInverseDocumentFrequency(String term)
    {
        //find the  no. of document that contains the term in whole document collection
        int count = 0;
        for(String doc : documentCollection)
        {
          count += getFrequencyInOneDoc(doc, term);
        }
        /*
         * log of the ratio of  total no of document in the collection to the no. of document containing the term
         * we can also use Math.Log(count/(1+documentCollection.Count)) to deal with divide by zero case; 
         */
        return (float)Math.log((float)documentCollection.size() / (float)count);
 
    }

public static float findCosineSimilarity(float[] vecA, float[] vecB)
{
    float dotProduct = dotProduct(vecA, vecB);
    float magnitudeOfA = magnitude(vecA);
    float magnitudeOfB = magnitude(vecB);
    float result = dotProduct / (magnitudeOfA * magnitudeOfB);
    //when 0 is divided by 0 it shows result NaN so return 0 in such case.
    if (Float.isNaN(result))
        return 0;
    else
        return (float)result;
}
 
public static float dotProduct(float[] vecA, float[] vecB)
{
 
    float dotProduct = 0;
    for (int i = 0; i < vecA.length; i++)
    {
        dotProduct += (vecA[i] * vecB[i]);
    }
 
    return dotProduct;
}
 
// Magnitude of the vector is the square root of the dot product of the vector with itself.
public static float magnitude(float[] vector)
{
    return (float)Math.sqrt(dotProduct(vector, vector));
}