void DatabaseConnectorTest::assertCorrectMockNgramTable(NgramTable ngramTable)
{
CPPUNIT_ASSERT_EQUAL(size_t(3), ngramTable.size());
CPPUNIT_ASSERT(ngramTable[0][0] == "foo");
CPPUNIT_ASSERT(ngramTable[0][1] == "bar");
CPPUNIT_ASSERT(ngramTable[0][2] == "foobar");
CPPUNIT_ASSERT(ngramTable[0][3] == "3");
CPPUNIT_ASSERT(ngramTable[1][0] == "bar");
CPPUNIT_ASSERT(ngramTable[1][1] == "foo");
CPPUNIT_ASSERT(ngramTable[1][2] == "foobar");
CPPUNIT_ASSERT(ngramTable[1][3] == "33");
CPPUNIT_ASSERT(ngramTable[2][0] == "foobar");
CPPUNIT_ASSERT(ngramTable[2][1] == "bar");
CPPUNIT_ASSERT(ngramTable[2][2] == "foo");
CPPUNIT_ASSERT(ngramTable[2][3] == "333");
}
Prediction SmoothedNgramPredictor::predict(const size_t max_partial_prediction_size, const char** filter) const
{
logger << DEBUG << "predict()" << endl;
// Result prediction
Prediction prediction;
// Cache all the needed tokens.
// tokens[k] corresponds to w_{i-k} in the generalized smoothed
// n-gram probability formula
//
std::vector<std::string> tokens(cardinality);
for (int i = 0; i < cardinality; i++) {
tokens[cardinality - 1 - i] = contextTracker->getToken(i);
logger << DEBUG << "Cached tokens[" << cardinality - 1 - i << "] = " << tokens[cardinality - 1 - i] << endl;
}
// Generate list of prefix completition candidates.
//
// The prefix completion candidates used to be obtained from the
// _1_gram table because in a well-constructed ngram database the
// _1_gram table (which contains all known tokens). However, this
// introduced a skew, since the unigram counts will take
// precedence over the higher-order counts.
//
// The current solution retrieves candidates from the highest
// n-gram table, falling back on lower order n-gram tables if
// initial completion set is smaller than required.
//
std::vector<std::string> prefixCompletionCandidates;
for (size_t k = cardinality; (k > 0 && prefixCompletionCandidates.size() < max_partial_prediction_size); k--) {
logger << DEBUG << "Building partial prefix completion table of cardinality: " << k << endl;
// create n-gram used to retrieve initial prefix completion table
Ngram prefix_ngram(k);
copy(tokens.end() - k, tokens.end(), prefix_ngram.begin());
if (logger.shouldLog()) {
logger << DEBUG << "prefix_ngram: ";
for (size_t r = 0; r < prefix_ngram.size(); r++) {
logger << DEBUG << prefix_ngram[r] << ' ';
}
logger << DEBUG << endl;
}
// obtain initial prefix completion candidates
db->beginTransaction();
NgramTable partial;
if (filter == 0) {
partial = db->getNgramLikeTable(prefix_ngram,max_partial_prediction_size - prefixCompletionCandidates.size());
} else {
partial = db->getNgramLikeTableFiltered(prefix_ngram,filter, max_partial_prediction_size - prefixCompletionCandidates.size());
}
db->endTransaction();
if (logger.shouldLog()) {
logger << DEBUG << "partial prefixCompletionCandidates" << endl
<< DEBUG << "----------------------------------" << endl;
for (size_t j = 0; j < partial.size(); j++) {
for (size_t k = 0; k < partial[j].size(); k++) {
logger << DEBUG << partial[j][k] << " ";
}
logger << endl;
}
}
logger << DEBUG << "Partial prefix completion table contains " << partial.size() << " potential completions." << endl;
// append newly discovered potential completions to prefix
// completion candidates array to fill it up to
// max_partial_prediction_size
//
std::vector<Ngram>::const_iterator it = partial.begin();
while (it != partial.end() && prefixCompletionCandidates.size() < max_partial_prediction_size) {
// only add new candidates, iterator it points to Ngram,
// it->end() - 2 points to the token candidate
//
std::string candidate = *(it->end() - 2);
if (find(prefixCompletionCandidates.begin(),
prefixCompletionCandidates.end(),
candidate) == prefixCompletionCandidates.end()) {
prefixCompletionCandidates.push_back(candidate);
}
it++;
}
}
if (logger.shouldLog()) {
logger << DEBUG << "prefixCompletionCandidates" << endl
<< DEBUG << "--------------------------" << endl;
for (size_t j = 0; j < prefixCompletionCandidates.size(); j++) {
logger << DEBUG << prefixCompletionCandidates[j] << endl;
}
}
// compute smoothed probabilities for all candidates
//
db->beginTransaction();
// getUnigramCountsSum is an expensive SQL query
// caching it here saves much time later inside the loop
int unigrams_counts_sum = db->getUnigramCountsSum();
for (size_t j = 0; (j < prefixCompletionCandidates.size() && j < max_partial_prediction_size); j++) {
// store w_i candidate at end of tokens
tokens[cardinality - 1] = prefixCompletionCandidates[j];
logger << DEBUG << "------------------" << endl;
logger << DEBUG << "w_i: " << tokens[cardinality - 1] << endl;
double probability = 0;
for (int k = 0; k < cardinality; k++) {
double numerator = count(tokens, 0, k+1);
// reuse cached unigrams_counts_sum to speed things up
double denominator = (k == 0 ? unigrams_counts_sum : count(tokens, -1, k));
double frequency = ((denominator > 0) ? (numerator / denominator) : 0);
probability += deltas[k] * frequency;
logger << DEBUG << "numerator: " << numerator << endl;
logger << DEBUG << "denominator: " << denominator << endl;
logger << DEBUG << "frequency: " << frequency << endl;
logger << DEBUG << "delta: " << deltas[k] << endl;
// for some sanity checks
assert(numerator <= denominator);
assert(frequency <= 1);
}
logger << DEBUG << "____________" << endl;
logger << DEBUG << "probability: " << probability << endl;
if (probability > 0) {
prediction.addSuggestion(Suggestion(tokens[cardinality - 1], probability));
}
}
db->endTransaction();
logger << DEBUG << "Prediction:" << endl;
logger << DEBUG << "-----------" << endl;
logger << DEBUG << prediction << endl;
return prediction;
}
