/*
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* Copyright (C) 2018 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef LIBTEXTCLASSIFIER_UTILS_TOKEN_FEATURE_EXTRACTOR_H_
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#define LIBTEXTCLASSIFIER_UTILS_TOKEN_FEATURE_EXTRACTOR_H_
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#include <memory>
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#include <unordered_set>
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#include <vector>
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#include "annotator/types.h"
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#include "utils/strings/stringpiece.h"
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#include "utils/utf8/unilib.h"
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namespace libtextclassifier3 {
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struct TokenFeatureExtractorOptions {
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// Number of buckets used for hashing charactergrams.
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int num_buckets = 0;
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// Orders of charactergrams to extract. E.g., 2 means character bigrams, 3
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// character trigrams etc.
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std::vector<int> chargram_orders;
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// Whether to extract the token case feature.
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bool extract_case_feature = false;
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// If true, will use the unicode-aware functionality for extracting features.
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bool unicode_aware_features = false;
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// Whether to extract the selection mask feature.
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bool extract_selection_mask_feature = false;
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// Regexp features to extract.
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std::vector<std::string> regexp_features;
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// Whether to remap digits to a single number.
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bool remap_digits = false;
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// Whether to lowercase all tokens.
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bool lowercase_tokens = false;
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// Maximum length of a word.
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int max_word_length = 20;
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// List of allowed charactergrams. The extracted charactergrams are filtered
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// using this list, and charactergrams that are not present are interpreted as
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// out-of-vocabulary.
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// If no allowed_chargrams are specified, all charactergrams are allowed.
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std::unordered_set<std::string> allowed_chargrams;
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};
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class TokenFeatureExtractor {
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public:
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TokenFeatureExtractor(const TokenFeatureExtractorOptions& options,
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const UniLib& unilib);
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// Extracts both the sparse (charactergram) and the dense features from a
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// token. is_in_span is a bool indicator whether the token is a part of the
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// selection span (true) or not (false).
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// The sparse_features output is optional. Fails and returns false if
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// dense_fatures in a nullptr.
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bool Extract(const Token& token, bool is_in_span,
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std::vector<int>* sparse_features,
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std::vector<float>* dense_features) const;
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// Extracts the sparse (charactergram) features from the token.
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std::vector<int> ExtractCharactergramFeatures(const Token& token) const;
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// Extracts the dense features from the token. is_in_span is a bool indicator
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// whether the token is a part of the selection span (true) or not (false).
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std::vector<float> ExtractDenseFeatures(const Token& token,
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bool is_in_span) const;
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int DenseFeaturesCount() const {
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int feature_count =
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options_.extract_case_feature + options_.extract_selection_mask_feature;
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feature_count += regex_patterns_.size();
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return feature_count;
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}
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protected:
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// Hashes given token to given number of buckets.
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int HashToken(StringPiece token) const;
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// Extracts the charactergram features from the token in a non-unicode-aware
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// way.
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std::vector<int> ExtractCharactergramFeaturesAscii(const Token& token) const;
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// Extracts the charactergram features from the token in a unicode-aware way.
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std::vector<int> ExtractCharactergramFeaturesUnicode(
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const Token& token) const;
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private:
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TokenFeatureExtractorOptions options_;
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std::vector<std::unique_ptr<UniLib::RegexPattern>> regex_patterns_;
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const UniLib& unilib_;
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};
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} // namespace libtextclassifier3
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#endif // LIBTEXTCLASSIFIER_UTILS_TOKEN_FEATURE_EXTRACTOR_H_
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