1 files changed, 126 insertions, 0 deletions
diff --git a/extractor/translation_table.cc b/extractor/translation_table.cc
new file mode 100644
index 00000000..45da707a
--- /dev/null
+++ b/extractor/translation_table.cc
@@ -0,0 +1,126 @@
+#include "translation_table.h"
+
+#include <string>
+#include <vector>
+
+#include <boost/functional/hash.hpp>
+
+#include "alignment.h"
+#include "data_array.h"
+
+using namespace std;
+
+namespace extractor {
+
+TranslationTable::TranslationTable(shared_ptr<DataArray> source_data_array,
+                                   shared_ptr<DataArray> target_data_array,
+                                   shared_ptr<Alignment> alignment) :
+    source_data_array(source_data_array), target_data_array(target_data_array) {
+  const vector<int>& source_data = source_data_array->GetData();
+  const vector<int>& target_data = target_data_array->GetData();
+
+  unordered_map<int, int> source_links_count;
+  unordered_map<int, int> target_links_count;
+  unordered_map<pair<int, int>, int, PairHash> links_count;
+
+  // For each pair of aligned source target words increment their link count by
+  // 1. Unaligned words are paired with the NULL token.
+  for (size_t i = 0; i < source_data_array->GetNumSentences(); ++i) {
+    vector<pair<int, int> > links = alignment->GetLinks(i);
+    int source_start = source_data_array->GetSentenceStart(i);
+    int target_start = target_data_array->GetSentenceStart(i);
+    // Ignore END_OF_LINE markers.
+    int next_source_start = source_data_array->GetSentenceStart(i + 1) - 1;
+    int next_target_start = target_data_array->GetSentenceStart(i + 1) - 1;
+    vector<int> source_sentence(source_data.begin() + source_start,
+        source_data.begin() + next_source_start);
+    vector<int> target_sentence(target_data.begin() + target_start,
+        target_data.begin() + next_target_start);
+    vector<int> source_linked_words(source_sentence.size());
+    vector<int> target_linked_words(target_sentence.size());
+
+    for (pair<int, int> link: links) {
+      source_linked_words[link.first] = 1;
+      target_linked_words[link.second] = 1;
+      IncrementLinksCount(source_links_count, target_links_count, links_count,
+          source_sentence[link.first], target_sentence[link.second]);
+    }
+
+    for (size_t i = 0; i < source_sentence.size(); ++i) {
+      if (!source_linked_words[i]) {
+        IncrementLinksCount(source_links_count, target_links_count, links_count,
+                            source_sentence[i], DataArray::NULL_WORD);
+      }
+    }
+
+    for (size_t i = 0; i < target_sentence.size(); ++i) {
+      if (!target_linked_words[i]) {
+        IncrementLinksCount(source_links_count, target_links_count, links_count,
+                            DataArray::NULL_WORD, target_sentence[i]);
+      }
+    }
+  }
+
+  // Calculating:
+  //   p(e | f) = count(e, f) / count(f)
+  //   p(f | e) = count(e, f) / count(e)
+  for (pair<pair<int, int>, int> link_count: links_count) {
+    int source_word = link_count.first.first;
+    int target_word = link_count.first.second;
+    double score1 = 1.0 * link_count.second / source_links_count[source_word];
+    double score2 = 1.0 * link_count.second / target_links_count[target_word];
+    translation_probabilities[link_count.first] = make_pair(score1, score2);
+  }
+}
+
+TranslationTable::TranslationTable() {}
+
+TranslationTable::~TranslationTable() {}
+
+void TranslationTable::IncrementLinksCount(
+    unordered_map<int, int>& source_links_count,
+    unordered_map<int, int>& target_links_count,
+    unordered_map<pair<int, int>, int, PairHash>& links_count,
+    int source_word_id,
+    int target_word_id) const {
+  ++source_links_count[source_word_id];
+  ++target_links_count[target_word_id];
+  ++links_count[make_pair(source_word_id, target_word_id)];
+}
+
+double TranslationTable::GetTargetGivenSourceScore(
+    const string& source_word, const string& target_word) {
+  if (!source_data_array->HasWord(source_word) ||
+      !target_data_array->HasWord(target_word)) {
+    return -1;
+  }
+
+  int source_id = source_data_array->GetWordId(source_word);
+  int target_id = target_data_array->GetWordId(target_word);
+  return translation_probabilities[make_pair(source_id, target_id)].first;
+}
+
+double TranslationTable::GetSourceGivenTargetScore(
+    const string& source_word, const string& target_word) {
+  if (!source_data_array->HasWord(source_word) ||
+      !target_data_array->HasWord(target_word)) {
+    return -1;
+  }
+
+  int source_id = source_data_array->GetWordId(source_word);
+  int target_id = target_data_array->GetWordId(target_word);
+  return translation_probabilities[make_pair(source_id, target_id)].second;
+}
+
+void TranslationTable::WriteBinary(const fs::path& filepath) const {
+  FILE* file = fopen(filepath.string().c_str(), "w");
+
+  int size = translation_probabilities.size();
+  fwrite(&size, sizeof(int), 1, file);
+  for (auto entry: translation_probabilities) {
+    fwrite(&entry.first, sizeof(entry.first), 1, file);
+    fwrite(&entry.second, sizeof(entry.second), 1, file);
+  }
+}
+
+} // namespace extractor