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#include "ns.h"
#include "ns_ter.h"
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <iostream>
#include <sstream>
using namespace std;
using boost::shared_ptr;
map<string, EvaluationMetric*> EvaluationMetric::instances_;
SegmentEvaluator::~SegmentEvaluator() {}
EvaluationMetric::~EvaluationMetric() {}
struct DefaultSegmentEvaluator : public SegmentEvaluator {
DefaultSegmentEvaluator(const vector<vector<WordID> >& refs, const EvaluationMetric* em) : refs_(refs), em_(em) {}
void Evaluate(const vector<WordID>& hyp, SufficientStats* out) const {
em_->ComputeSufficientStatistics(hyp, refs_, out);
}
const vector<vector<WordID> > refs_;
const EvaluationMetric* em_;
};
shared_ptr<SegmentEvaluator> EvaluationMetric::CreateSegmentEvaluator(const vector<vector<WordID> >& refs) const {
return shared_ptr<SegmentEvaluator>(new DefaultSegmentEvaluator(refs, this));
}
void EvaluationMetric::ComputeSufficientStatistics(const vector<WordID>&,
const vector<vector<WordID> >&,
SufficientStats*) const {
cerr << "Base class ComputeSufficientStatistics should not be called.\n";
abort();
}
enum BleuType { IBM, Koehn, NIST };
template <unsigned int N = 4u, BleuType BrevityType = IBM>
struct BleuSegmentEvaluator : public SegmentEvaluator {
BleuSegmentEvaluator(const vector<vector<WordID> >& refs, const EvaluationMetric* em) : evaluation_metric(em) {
assert(refs.size() > 0);
float tot = 0;
int smallest = 9999999;
for (vector<vector<WordID> >::const_iterator ci = refs.begin();
ci != refs.end(); ++ci) {
lengths_.push_back(ci->size());
tot += lengths_.back();
if (lengths_.back() < smallest) smallest = lengths_.back();
CountRef(*ci);
}
if (BrevityType == Koehn)
lengths_[0] = tot / refs.size();
if (BrevityType == NIST)
lengths_[0] = smallest;
}
void Evaluate(const vector<WordID>& hyp, SufficientStats* out) const {
out->fields.resize(N + N + 2);
out->evaluation_metric = evaluation_metric;
for (unsigned i = 0; i < N+N+2; ++i) out->fields[i] = 0;
ComputeNgramStats(hyp, &out->fields[0], &out->fields[N], true);
float& hyp_len = out->fields[2*N];
float& ref_len = out->fields[2*N + 1];
hyp_len = hyp.size();
ref_len = lengths_[0];
if (lengths_.size() > 1 && BrevityType == IBM) {
float bestd = 2000000;
float hl = hyp.size();
float bl = -1;
for (vector<float>::const_iterator ci = lengths_.begin(); ci != lengths_.end(); ++ci) {
if (fabs(*ci - hl) < bestd) {
bestd = fabs(*ci - hl);
bl = *ci;
}
}
ref_len = bl;
}
}
struct NGramCompare {
int operator() (const vector<WordID>& a, const vector<WordID>& b) {
const size_t as = a.size();
const size_t bs = b.size();
const size_t s = (as < bs ? as : bs);
for (size_t i = 0; i < s; ++i) {
int d = a[i] - b[i];
if (d < 0) return true;
if (d > 0) return false;
}
return as < bs;
}
};
typedef map<vector<WordID>, pair<int,int>, NGramCompare> NGramCountMap;
void CountRef(const vector<WordID>& ref) {
NGramCountMap tc;
vector<WordID> ngram(N);
int s = ref.size();
for (int j=0; j<s; ++j) {
int remaining = s-j;
int k = (N < remaining ? N : remaining);
ngram.clear();
for (int i=1; i<=k; ++i) {
ngram.push_back(ref[j + i - 1]);
tc[ngram].first++;
}
}
for (typename NGramCountMap::iterator i = tc.begin(); i != tc.end(); ++i) {
pair<int,int>& p = ngrams_[i->first];
if (p.first < i->second.first)
p = i->second;
}
}
void ComputeNgramStats(const vector<WordID>& sent,
float* correct, // N elements reserved
float* hyp, // N elements reserved
bool clip_counts = true) const {
vector<WordID> ngram(N);
*correct *= 0;
*hyp *= 0;
int s = sent.size();
for (int j=0; j<s; ++j) {
int remaining = s-j;
int k = (N < remaining ? N : remaining);
ngram.clear();
for (int i=1; i<=k; ++i) {
ngram.push_back(sent[j + i - 1]);
pair<int,int>& p = ngrams_[ngram];
if(clip_counts){
if (p.second < p.first) {
++p.second;
correct[i-1]++;
}
} else {
++p.second;
correct[i-1]++;
}
// if the 1 gram isn't found, don't try to match don't need to match any 2- 3- .. grams:
if (!p.first) {
for (; i<=k; ++i)
hyp[i-1]++;
} else {
hyp[i-1]++;
}
}
}
}
const EvaluationMetric* evaluation_metric;
vector<float> lengths_;
mutable NGramCountMap ngrams_;
};
template <unsigned int N = 4u, BleuType BrevityType = IBM>
struct BleuMetric : public EvaluationMetric {
BleuMetric() : EvaluationMetric("IBM_BLEU") {}
float ComputeScore(const SufficientStats& stats) const {
float log_bleu = 0;
int count = 0;
for (int i = 0; i < N; ++i) {
if (stats.fields[i+N] > 0) {
float cor_count = stats.fields[i]; // correct_ngram_hit_counts[i];
// smooth bleu
if (!cor_count) { cor_count = 0.01; }
float lprec = log(cor_count) - log(stats.fields[i+N]); // log(hyp_ngram_counts[i]);
// if (precs) precs->push_back(exp(lprec));
log_bleu += lprec;
++count;
}
}
log_bleu /= count;
float lbp = 0.0;
const float& hyp_len = stats.fields[2*N];
const float& ref_len = stats.fields[2*N + 1];
if (hyp_len < ref_len)
lbp = (hyp_len - ref_len) / hyp_len;
log_bleu += lbp;
//if (bp) *bp = exp(lbp);
return exp(log_bleu);
}
shared_ptr<SegmentEvaluator> CreateSegmentEvaluator(const vector<vector<WordID> >& refs) const {
return shared_ptr<SegmentEvaluator>(new BleuSegmentEvaluator<N,BrevityType>(refs, this));
}
};
EvaluationMetric* EvaluationMetric::Instance(const string& metric_id) {
static bool is_first = true;
if (is_first) {
instances_["NULL"] = NULL;
is_first = false;
}
map<string, EvaluationMetric*>::iterator it = instances_.find(metric_id);
if (it == instances_.end()) {
EvaluationMetric* m = NULL;
if (metric_id == "IBM_BLEU") {
m = new BleuMetric<4, IBM>;
} else if (metric_id == "NIST_BLEU") {
m = new BleuMetric<4, NIST>;
} else if (metric_id == "Koehn_BLEU") {
m = new BleuMetric<4, Koehn>;
} else if (metric_id == "TER") {
m = new TERMetric;
} else {
cerr << "Implement please: " << metric_id << endl;
abort();
}
if (m->MetricId() != metric_id) {
cerr << "Registry error: " << metric_id << " vs. " << m->MetricId() << endl;
abort();
}
return instances_[metric_id] = m;
} else {
return it->second;
}
}
SufficientStats::SufficientStats(const string& encoded) {
istringstream is(encoded);
string type;
is >> type;
evaluation_metric = EvaluationMetric::Instance(type);
float val;
while(is >> val)
fields.push_back(val);
}
void SufficientStats::Encode(string* out) const {
ostringstream os;
if (evaluation_metric)
os << evaluation_metric->MetricId();
else
os << "NULL";
for (unsigned i = 0; i < fields.size(); ++i)
os << ' ' << fields[i];
*out = os.str();
}
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