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#ifndef MERT_NGRAM_H_
#define MERT_NGRAM_H_
#include <vector>
#include <map>
#include <string>
/** 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 {
std::size_t i;
const std::size_t as = a.size();
const std::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;
}
}
/**
* 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;
}
/**
* 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.
*/
std::size_t size() const { return m_counts.size(); }
std::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; }
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_
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