Create a header file for NgramCounts class.

The reason is that we want to add the unit test.

1 files changed, 97 insertions, 0 deletions

diff --git a/mert/Ngram.h b/mert/Ngram.h
new file mode 100644
index 000000000..493ef5de8
--- /dev/null
+++ b/mert/Ngram.h
@@ -0,0 +1,97 @@
+#ifndef MERT_NGRAM_H_
+#define MERT_NGRAM_H_
+
+#include <vector>
+#include <map>
+
+/** A simple STL-std::map based n-gram counts. Basically, we provide
+ * typical accessors and mutaors, but we intentionally does not allow
+ * erasing elements.
+ */
+class NgramCounts {
+ public:
+  // Used to construct the ngram map
+  struct NgramComparator {
+    bool operator()(const std::vector<int>& a, const std::vector<int>& b) const {
+      size_t i;
+      const size_t as = a.size();
+      const size_t bs = b.size();
+      for (i = 0; i < as && i < bs; ++i) {
+        if (a[i] < b[i]) {
+          return true;
+        }
+        if (a[i] > b[i]) {
+          return false;
+        }
+      }
+      // entries are equal, shortest wins
+      return as < bs;
+    }
+  };
+
+  typedef std::vector<int> Key;
+  typedef int Value;
+  typedef std::map<Key, Value, NgramComparator>::iterator iterator;
+  typedef std::map<Key, Value, NgramComparator>::const_iterator const_iterator;
+
+  NgramCounts() : kDefaultCount(1) { }
+  virtual ~NgramCounts() { }
+
+  /**
+   * If the specified "ngram" is found, we add counts.
+   * If not, we insert the default count in the container. */
+  void add(const Key& ngram) {
+    const_iterator it = find(ngram);
+    if (it != end()) {
+      m_counts[ngram] = it->second + 1;
+    } else {
+      m_counts[ngram] = kDefaultCount;
+    }
+  }
+
+  /**
+   * Clear all elments in the container.
+   */
+  void clear() { m_counts.clear(); }
+
+  /**
+   * Return true iff the container is empty.
+   */
+  bool empty() const { return m_counts.empty(); }
+
+  /**
+   * Return the the number of elements in the container.
+   */
+  size_t size() const { return m_counts.size(); }
+
+  size_t max_size() const { return m_counts.max_size(); }
+
+  // Note: This is mainly used by unit tests.
+  int get_default_count() const { return kDefaultCount; }
+
+  /**
+   * Return true iff the specified "ngram" is found in the container.
+   */
+  bool lookup(const Key& ngram, Value* v) const {
+    const_iterator it = m_counts.find(ngram);
+    if (it == m_counts.end()) return false;
+    *v = it->second;
+    return true;
+  }
+
+  iterator find(const Key& ngram) { return m_counts.find(ngram); }
+  const_iterator find(const Key& ngram) const { return m_counts.find(ngram); }
+
+  Value& operator[](const Key& ngram) { return m_counts[ngram]; }
+
+  iterator begin() { return m_counts.begin(); }
+  const_iterator begin() const { return m_counts.begin(); }
+  iterator end() { return m_counts.end(); }
+  const_iterator end() const { return m_counts.end(); }
+
+ private:
+  const int kDefaultCount;
+  std::map<Key, Value, NgramComparator> m_counts;
+};
+
+#endif  // MERT_NGRAM_H_