/**
* Note: the BM25 kernel places interpretations on the two objects compared...
*
* @return BM25 similarity between query and document, and query should always come first.
*/
public double sim(Object objQuery, Object objDoc) {
// Will modify in place, so need to copy
Map<Object, Double> query = VectorUtils.Copy((Map<Object, Double>) objQuery);
Map<Object, Double> doc = VectorUtils.Copy((Map<Object, Double>) objDoc);
// Modify query according to BM25 kernel
for (Object key : query.keySet()) {
double freq = query.get(key);
freq = ((_k3 + 1) * freq) / (_k3 + freq);
Double idf = _hmKey2IDF.get(key);
if (idf == null) idf = _dDefaultIDF;
query.put(key, freq * idf);
}
// Modify doc according to BM25 kernel
double doc_length_ratio = VectorUtils.L1Norm(doc) / _dAvgDocLength;
for (Object key : doc.keySet()) {
double freq = doc.get(key);
freq = ((_k1 + 1) * freq) / (_k1 * (1d - _b + _b * doc_length_ratio) + freq);
doc.put(key, freq);
}
return VectorUtils.DotProduct(query, doc);
}
/** * */
/// *
public double sim(Object o1, Object o2, Object ow) {
System.out.println("ERROR: Cannot do BM25 query-reweighted similarity");
System.exit(1);
return -1d;
}
// */
public double sim_(Object o1, Object o2, Object ow) {
Map<Object, Double> map1 = (Map<Object, Double>) o1;
Map<Object, Double> map2 = (Map<Object, Double>) o2;
Map<Object, Double> query;
Map<Object, Double> doc;
if (map1.size() < map2.size()) {
query = VectorUtils.Copy(map1);
doc = VectorUtils.Copy(map2);
} else {
query = VectorUtils.Copy(map2);
doc = VectorUtils.Copy(map1);
}
// Modify query according to BM25 kernel
for (Object key : query.keySet()) {
double freq = query.get(key);
freq = ((_k3 + 1) * freq) / (_k3 + freq);
Double idf = _hmKey2IDF.get(key);
if (idf == null) idf = _dDefaultIDF;
query.put(key, freq * idf);
}
// Modify doc according to BM25 kernel
double doc_length_ratio = VectorUtils.L1Norm(doc) / _dAvgDocLength;
for (Object key : doc.keySet()) {
double freq = doc.get(key);
freq = ((_k1 + 1) * freq) / (_k1 * (1d - _b + _b * doc_length_ratio) + freq);
doc.put(key, freq);
}
return VectorUtils.DotProduct(query, doc);
}
public void initTonNDocs(Set<String> docs_topn) {
if (docs_topn == _mPrevInit) return; // Already initialized
_mPrevInit = docs_topn;
_hmKey2IDF = new HashMap<Object, Double>();
double total_doc_length = 0d;
// Have to go through all documents to compute term IDF
for (String doc : docs_topn) {
// Map<Object,Double> features = (Map<Object,Double>)getObjectRepresentation(doc);
Map<Object, Double> features = DocUtils.ConvertToFeatureMap(_docs_all.get(doc));
//
total_doc_length += VectorUtils.L1Norm(features);
//
features = VectorUtils.ConvertToBoolean(features);
//
_hmKey2IDF = VectorUtils.Sum(_hmKey2IDF, features);
/*
if (false && ++i % 100 == 0) {
System.out.println("- Converted " + i + " documents to internal representation");
System.out.flush();
}
*/
}
_dAvgDocLength = total_doc_length / (double) docs_topn.size();
for (Object key : _hmKey2IDF.keySet()) {
Double idf = docs_topn.size() / (_hmKey2IDF.get(key) + 1d);
_hmKey2IDF.put(key, Math.log(idf));
}
_dDefaultIDF = Math.log(docs_topn.size() / 1d);
if (DEBUG) {
System.out.println("Avg doc length: " + _dAvgDocLength);
System.out.println("Default IDF : " + _dDefaultIDF);
System.out.println("IDF after log: " + _hmKey2IDF);
}
}
