}
// Pearson's product-moment coefficient
private double correlation(int a, int b) throws IOException {
double score = 0;
TermFreqVector doc_a = reader.getTermFreqVector(a, docDataField);
// /////////////
// if( doc_a==null) System.out.println("doc_a is null");
// /////////////
TermFreqVector doc_b = reader.getTermFreqVector(b, docDataField);
// stroe all the term freq in hashmap
HashMap term_map = new HashMap();
HashMap map_a = new HashMap();
String terms[] = doc_a.getTerms();
int freq[] = doc_a.getTermFrequencies();
double ave_a = 0;
for (int i = 0; i < terms.length; i++) {
map_a.put(terms[i], freq[i]);
term_map.put(terms[i], terms[i]);
ave_a += freq[i];
}
ave_a = ave_a / terms.length;
double ave_b = 0;
HashMap map_b = new HashMap();
terms = doc_b.getTerms();
freq = doc_b.getTermFrequencies();
for (int i = 0; i < terms.length; i++) {
map_b.put(terms[i], freq[i]);
term_map.put(terms[i], terms[i]);
ave_b += freq[i];
}