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#include "ff.h"
#include <iostream>
#include <sstream>
using namespace std;
// example of a "stateful" feature made available as an external library
// This feature looks nodes and their daughters and fires an indicator based
// on the arities of the rules involved.
// (X (X a) b (X c)) - this is a 2 arity parent with children of 0 and 0 arity
// so you get MAF_2_0_0=1
class ParentChildrenArityFeatures : public FeatureFunction {
public:
ParentChildrenArityFeatures(const string& param) : fids(16, vector<int>(256, -1)) {
SetStateSize(1); // number of bytes extra state required by this Feature
}
virtual void FinalTraversalFeatures(const void* context,
SparseVector<double>* features) const {
// Goal always is arity 1, so there's no discriminative value of
// computing a feature
}
protected:
virtual void TraversalFeaturesImpl(const SentenceMetadata& smeta,
const Hypergraph::Edge& edge,
const std::vector<const void*>& ant_contexts,
FeatureVector* features,
FeatureVector* estimated_features,
void* context) const {
unsigned child_arity_code = 0;
for (unsigned j = 0; j < ant_contexts.size(); ++j) {
child_arity_code <<= 4;
child_arity_code |= *reinterpret_cast<const unsigned char*>(ant_contexts[j]);
}
int& fid = fids[edge.Arity()][child_arity_code]; // reference!
if (fid < 0) {
ostringstream feature_string;
feature_string << "MAF_" << edge.Arity();
for (unsigned j = 0; j < ant_contexts.size(); ++j)
feature_string << '_' <<
static_cast<int>(*reinterpret_cast<const unsigned char*>(ant_contexts[j]));
fid = FD::Convert(feature_string.str());
}
features->set_value(fid, 1.0);
*reinterpret_cast<unsigned char*>(context) = edge.Arity(); // save state
}
private:
mutable vector<vector<int> > fids;
};
// IMPORTANT: this function must be implemented by any external FF library
// if your library has multiple features, you can use str to configure things
extern "C" FeatureFunction* create_ff(const string& str) {
return new ParentChildrenArityFeatures(str);
}
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