1 files changed, 46 insertions, 0 deletions
diff --git a/extractor/sampler.cc b/extractor/sampler.cc
new file mode 100644
index 00000000..d81956b5
--- /dev/null
+++ b/extractor/sampler.cc
@@ -0,0 +1,46 @@
+#include "sampler.h"
+
+#include "phrase_location.h"
+#include "suffix_array.h"
+
+namespace extractor {
+
+Sampler::Sampler(shared_ptr<SuffixArray> suffix_array, int max_samples) :
+    suffix_array(suffix_array), max_samples(max_samples) {}
+
+Sampler::Sampler() {}
+
+Sampler::~Sampler() {}
+
+PhraseLocation Sampler::Sample(const PhraseLocation& location) const {
+  vector<int> sample;
+  int num_subpatterns;
+  if (location.matchings == NULL) {
+    // Sample suffix array range.
+    num_subpatterns = 1;
+    int low = location.sa_low, high = location.sa_high;
+    double step = max(1.0, (double) (high - low) / max_samples);
+    for (double i = low; i < high && sample.size() < max_samples; i += step) {
+      sample.push_back(suffix_array->GetSuffix(Round(i)));
+    }
+  } else {
+    // Sample vector of occurrences.
+    num_subpatterns = location.num_subpatterns;
+    int num_matchings = location.matchings->size() / num_subpatterns;
+    double step = max(1.0, (double) num_matchings / max_samples);
+    for (double i = 0, num_samples = 0;
+         i < num_matchings && num_samples < max_samples;
+         i += step, ++num_samples) {
+      int start = Round(i) * num_subpatterns;
+      sample.insert(sample.end(), location.matchings->begin() + start,
+          location.matchings->begin() + start + num_subpatterns);
+    }
+  }
+  return PhraseLocation(sample, num_subpatterns);
+}
+
+int Sampler::Round(double x) const {
+  return x + 0.5;
+}
+
+} // namespace extractor