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#include "precomputation.h"
#include <iostream>
#include <queue>
#include "data_array.h"
#include "suffix_array.h"
using namespace std;
namespace extractor {
int Precomputation::FIRST_NONTERMINAL = -1;
int Precomputation::SECOND_NONTERMINAL = -2;
Precomputation::Precomputation(
shared_ptr<SuffixArray> suffix_array, int num_frequent_phrases,
int num_super_frequent_phrases, int max_rule_span,
int max_rule_symbols, int min_gap_size,
int max_frequent_phrase_len, int min_frequency) {
vector<int> data = suffix_array->GetData()->GetData();
vector<vector<int>> frequent_phrases = FindMostFrequentPhrases(
suffix_array, data, num_frequent_phrases, max_frequent_phrase_len,
min_frequency);
// Construct sets containing the frequent and superfrequent contiguous
// collocations.
unordered_set<vector<int>, VectorHash> frequent_phrases_set;
unordered_set<vector<int>, VectorHash> super_frequent_phrases_set;
for (size_t i = 0; i < frequent_phrases.size(); ++i) {
frequent_phrases_set.insert(frequent_phrases[i]);
if (i < num_super_frequent_phrases) {
super_frequent_phrases_set.insert(frequent_phrases[i]);
}
}
vector<tuple<int, int, int>> locations;
for (size_t i = 0; i < data.size(); ++i) {
// If the sentence is over, add all the discontiguous frequent phrases to
// the list.
if (data[i] == DataArray::END_OF_LINE) {
AddCollocations(locations, data, max_rule_span, min_gap_size,
max_rule_symbols);
locations.clear();
continue;
}
vector<int> phrase;
// Find all the contiguous frequent phrases starting at position i.
for (int j = 1; j <= max_frequent_phrase_len && i + j <= data.size(); ++j) {
phrase.push_back(data[i + j - 1]);
if (frequent_phrases_set.count(phrase)) {
int is_super_frequent = super_frequent_phrases_set.count(phrase);
locations.push_back(make_tuple(i, j, is_super_frequent));
} else {
// If the current phrase is not frequent, any longer phrase having the
// current phrase as prefix will not be frequent.
break;
}
}
}
collocations.shrink_to_fit();
}
Precomputation::Precomputation() {}
Precomputation::~Precomputation() {}
vector<vector<int>> Precomputation::FindMostFrequentPhrases(
shared_ptr<SuffixArray> suffix_array, const vector<int>& data,
int num_frequent_phrases, int max_frequent_phrase_len, int min_frequency) {
vector<int> lcp = suffix_array->BuildLCPArray();
vector<int> run_start(max_frequent_phrase_len);
// Find all the phrases occurring at least min_frequency times.
priority_queue<pair<int, pair<int, int>>> heap;
for (size_t i = 1; i < lcp.size(); ++i) {
for (int len = lcp[i]; len < max_frequent_phrase_len; ++len) {
int frequency = i - run_start[len];
if (frequency >= min_frequency) {
heap.push(make_pair(frequency,
make_pair(suffix_array->GetSuffix(run_start[len]), len + 1)));
}
run_start[len] = i;
}
}
// Extract the most frequent phrases.
vector<vector<int>> frequent_phrases;
while (frequent_phrases.size() < num_frequent_phrases && !heap.empty()) {
int start = heap.top().second.first;
int len = heap.top().second.second;
heap.pop();
vector<int> phrase(data.begin() + start, data.begin() + start + len);
if (find(phrase.begin(), phrase.end(), DataArray::END_OF_LINE) ==
phrase.end()) {
frequent_phrases.push_back(phrase);
}
}
return frequent_phrases;
}
void Precomputation::AddCollocations(
const vector<tuple<int, int, int>>& locations, const vector<int>& data,
int max_rule_span, int min_gap_size, int max_rule_symbols) {
// Select the leftmost subphrase.
for (size_t i = 0; i < locations.size(); ++i) {
int start1, size1, is_super1;
tie(start1, size1, is_super1) = locations[i];
// Select the second (middle) subphrase
for (size_t j = i + 1; j < locations.size(); ++j) {
int start2, size2, is_super2;
tie(start2, size2, is_super2) = locations[j];
if (start2 - start1 >= max_rule_span) {
break;
}
if (start2 - start1 - size1 >= min_gap_size
&& start2 + size2 - start1 <= max_rule_span
&& size1 + size2 + 1 <= max_rule_symbols) {
vector<int> collocation(data.begin() + start1,
data.begin() + start1 + size1);
collocation.push_back(Precomputation::FIRST_NONTERMINAL);
collocation.insert(collocation.end(), data.begin() + start2,
data.begin() + start2 + size2);
AddCollocation(collocation, GetLocation(start1, start2));
// Try extending the binary collocation to a ternary collocation.
if (is_super2) {
collocation.push_back(Precomputation::SECOND_NONTERMINAL);
// Select the rightmost subphrase.
for (size_t k = j + 1; k < locations.size(); ++k) {
int start3, size3, is_super3;
tie(start3, size3, is_super3) = locations[k];
if (start3 - start1 >= max_rule_span) {
break;
}
if (start3 - start2 - size2 >= min_gap_size
&& start3 + size3 - start1 <= max_rule_span
&& size1 + size2 + size3 + 2 <= max_rule_symbols
&& (is_super1 || is_super3)) {
collocation.insert(collocation.end(), data.begin() + start3,
data.begin() + start3 + size3);
AddCollocation(collocation, GetLocation(start1, start2, start3));
collocation.erase(collocation.end() - size3);
}
}
}
}
}
}
}
vector<int> Precomputation::GetLocation(int pos1, int pos2) {
vector<int> location;
location.push_back(pos1);
location.push_back(pos2);
return location;
}
vector<int> Precomputation::GetLocation(int pos1, int pos2, int pos3) {
vector<int> location;
location.push_back(pos1);
location.push_back(pos2);
location.push_back(pos3);
return location;
}
void Precomputation::AddCollocation(vector<int> collocation,
vector<int> location) {
collocation.shrink_to_fit();
location.shrink_to_fit();
collocations.push_back(make_pair(collocation, location));
}
Collocations Precomputation::GetCollocations() const {
return collocations;
}
bool Precomputation::operator==(const Precomputation& other) const {
return collocations == other.collocations;
}
} // namespace extractor
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