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* Copyright (C) 2017 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <memory>
#include <unordered_set>
#include <vector>
#include "types.h"
#include "util/strings/stringpiece.h"
#include "util/utf8/unilib.h"
namespace libtextclassifier2 {
struct TokenFeatureExtractorOptions {
// Number of buckets used for hashing charactergrams.
int num_buckets = 0;
// Orders of charactergrams to extract. E.g., 2 means character bigrams, 3
// character trigrams etc.
std::vector<int> chargram_orders;
// Whether to extract the token case feature.
bool extract_case_feature = false;
// If true, will use the unicode-aware functionality for extracting features.
bool unicode_aware_features = false;
// Whether to extract the selection mask feature.
bool extract_selection_mask_feature = false;
// Regexp features to extract.
std::vector<std::string> regexp_features;
// Whether to remap digits to a single number.
bool remap_digits = false;
// Whether to lowercase all tokens.
bool lowercase_tokens = false;
// Maximum length of a word.
int max_word_length = 20;
// List of allowed charactergrams. The extracted charactergrams are filtered
// using this list, and charactergrams that are not present are interpreted as
// out-of-vocabulary.
// If no allowed_chargrams are specified, all charactergrams are allowed.
std::unordered_set<std::string> allowed_chargrams;
class TokenFeatureExtractor {
TokenFeatureExtractor(const TokenFeatureExtractorOptions& options,
const UniLib& unilib);
// Extracts features from a token.
// - is_in_span is a bool indicator whether the token is a part of the
// selection span (true) or not (false).
// - sparse_features are indices into a sparse feature vector of size
// options.num_buckets which are set to 1.0 (others are implicitly 0.0).
// - dense_features are values of a dense feature vector of size 0-2
// (depending on the options) for the token
bool Extract(const Token& token, bool is_in_span,
std::vector<int>* sparse_features,
std::vector<float>* dense_features) const;
int DenseFeaturesCount() const {
int feature_count =
options_.extract_case_feature + options_.extract_selection_mask_feature;
feature_count += regex_patterns_.size();
return feature_count;
// Hashes given token to given number of buckets.
int HashToken(StringPiece token) const;
// Extracts the charactergram features from the token.
std::vector<int> ExtractCharactergramFeatures(const Token& token) const;
// Extracts the charactergram features from the token in a non-unicode-aware
// way.
std::vector<int> ExtractCharactergramFeaturesAscii(const Token& token) const;
// Extracts the charactergram features from the token in a unicode-aware way.
std::vector<int> ExtractCharactergramFeaturesUnicode(
const Token& token) const;
TokenFeatureExtractorOptions options_;
std::vector<std::unique_ptr<UniLib::RegexPattern>> regex_patterns_;
const UniLib& unilib_;
} // namespace libtextclassifier2