From 8cc05e205fd21c18e2091255413b96fc412e3ef8 Mon Sep 17 00:00:00 2001
From: Chris Dyer <cdyer@cs.cmu.edu>
Date: Sun, 6 Mar 2011 01:01:29 -0500
Subject: oov feature

---
 decoder/ff_klm.cc | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

(limited to 'decoder/ff_klm.cc')

diff --git a/decoder/ff_klm.cc b/decoder/ff_klm.cc
index 7c37ddb7..203bced5 100644
--- a/decoder/ff_klm.cc
+++ b/decoder/ff_klm.cc
@@ -82,11 +82,13 @@ class KLanguageModelImpl {
   }
 
  public:
-  double LookupWords(const TRule& rule, const vector<const void*>& ant_states, double* pest_sum, void* remnant) {
+  double LookupWords(const TRule& rule, const vector<const void*>& ant_states, double* pest_sum, double* oovs, double* est_oovs, void* remnant) {
     double sum = 0.0;
     double est_sum = 0.0;
     int num_scored = 0;
     int num_estimated = 0;
+    if (oovs) *oovs = 0;
+    if (est_oovs) *est_oovs = 0;
     bool saw_eos = false;
     bool has_some_history = false;
     lm::ngram::State state = ngram_->NullContextState();
@@ -98,6 +100,7 @@ class KLanguageModelImpl {
         int unscored_ant_len = UnscoredSize(astate);
         for (int k = 0; k < unscored_ant_len; ++k) {
           const lm::WordIndex cur_word = IthUnscoredWord(k, astate);
+          const bool is_oov = (cur_word == 0);
           double p = 0;
           if (cur_word == kSOS_) {
             state = ngram_->BeginSentenceState();
@@ -120,11 +123,13 @@ class KLanguageModelImpl {
           }
           if (context_complete) {
             sum += p;
+            if (oovs && is_oov) (*oovs)++;
           } else {
             if (remnant)
               SetIthUnscoredWord(num_estimated, cur_word, remnant);
             ++num_estimated;
             est_sum += p;
+            if (est_oovs && is_oov) (*est_oovs)++;
           }
         }
         saw_eos = GetFlag(astate, HAS_EOS_ON_RIGHT);
@@ -135,6 +140,7 @@ class KLanguageModelImpl {
       } else {   // handle terminal
         const lm::WordIndex cur_word = MapWord(e[j]);
         double p = 0;
+        const bool is_oov = (cur_word == 0);
         if (cur_word == kSOS_) {
           state = ngram_->BeginSentenceState();
           if (has_some_history) {  // this is immediately fully scored, and bad
@@ -156,11 +162,13 @@ class KLanguageModelImpl {
         }
         if (context_complete) {
           sum += p;
+          if (oovs && is_oov) (*oovs)++;
         } else {
           if (remnant)
             SetIthUnscoredWord(num_estimated, cur_word, remnant);
           ++num_estimated;
           est_sum += p;
+          if (est_oovs && is_oov) (*est_oovs)++;
         }
       }
     }
@@ -183,7 +191,7 @@ class KLanguageModelImpl {
       SetHasFullContext(1, dummy_state_);
       SetUnscoredSize(0, dummy_state_);
       dummy_ants_[1] = state;
-      return LookupWords(*dummy_rule_, dummy_ants_, NULL, NULL);
+      return LookupWords(*dummy_rule_, dummy_ants_, NULL, NULL, NULL, NULL);
     } else {  // rules DO produce <s> ... </s>
       double p = 0;
       if (!GetFlag(state, HAS_EOS_ON_RIGHT)) { p -= 100; }
@@ -264,7 +272,8 @@ class KLanguageModelImpl {
 template <class Model>
 KLanguageModel<Model>::KLanguageModel(const string& param) {
   pimpl_ = new KLanguageModelImpl<Model>(param);
-  fid_ = FD::Convert("LanguageModel");
+  fid_ = FD::Convert("LanguageModel");  // todo support LM feature name
+  oov_fid_ = FD::Convert("OOV");        // should also be named
   SetStateSize(pimpl_->ReserveStateSize());
 }
 
@@ -286,8 +295,14 @@ void KLanguageModel<Model>::TraversalFeaturesImpl(const SentenceMetadata& /* sme
                                           SparseVector<double>* estimated_features,
                                           void* state) const {
   double est = 0;
-  features->set_value(fid_, pimpl_->LookupWords(*edge.rule_, ant_states, &est, state));
+  double oovs = 0;
+  double est_oovs = 0;
+  features->set_value(fid_, pimpl_->LookupWords(*edge.rule_, ant_states, &est, &oovs, &est_oovs, state));
   estimated_features->set_value(fid_, est);
+  if (oov_fid_) {
+    if (oovs) features->set_value(oov_fid_, oovs);
+    if (est_oovs) estimated_features->set_value(oov_fid_, est_oovs);
+  }
 }
 
 template <class Model>
-- 
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