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#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 unordered_set<int>& blacklisted_sentence_ids) const {
shared_ptr<DataArray> source_data_array = suffix_array->GetData();
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);
double i = low, last = i - 1;
while (sample.size() < max_samples && i < high) {
int x = suffix_array->GetSuffix(Round(i));
int id = source_data_array->GetSentenceId(x);
bool found = false;
if (blacklisted_sentence_ids.count(id)) {
for (int backoff_step = 1; backoff_step <= step; ++backoff_step) {
double j = i - backoff_step;
x = suffix_array->GetSuffix(Round(j));
id = source_data_array->GetSentenceId(x);
if (x >= 0 && j > last && !blacklisted_sentence_ids.count(id)) {
found = true;
last = i;
break;
}
double k = i + backoff_step;
x = suffix_array->GetSuffix(Round(k));
id = source_data_array->GetSentenceId(x);
if (k < min(i+step, (double) high) &&
!blacklisted_sentence_ids.count(id)) {
found = true;
last = k;
break;
}
}
} else {
found = true;
last = i;
}
if (found) sample.push_back(x);
i += step;
}
} 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
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