Merge pull request #7 from irinakhismatullina/encode

Encoding API

Author: vmarkovtsev

bpe.go

@@ -2,6 +2,7 @@ package bpe
 
 import (
 	"bufio"
+	"container/heap"
 	"encoding/binary"
 	"errors"
 	"io"
@@ -14,6 +15,9 @@ import (
 // TokenID is a numerical identifier of the subword token
 type TokenID uint32
 
+// TokenIDPair is a concatenation of two TokenIDs that is used as the key type in rule2id map.
+type TokenIDPair uint64
+
 // EncodedString is a sequence of subword token identifiers
 type EncodedString []TokenID
 
@@ -24,6 +28,13 @@ const (
 	eosToken = "<EOS>"
 )
 
+// EncodingConfig is a configuration for encoding of strings
+type EncodingConfig struct {
+	bos     bool
+	eos     bool
+	reverse bool
+}
+
 type rule struct {
 	left   TokenID
 	right  TokenID
@@ -43,6 +54,7 @@ type Model struct {
 	char2id       map[rune]TokenID
 	id2char       map[TokenID]rune
 	rules         []rule
+	rule2id       map[TokenIDPair]int
 	recipe        map[TokenID]EncodedString
 	revRecipe     map[string]TokenID
 	specialTokens specialTokens
@@ -54,13 +66,18 @@ func newModel(nRules int) *Model {
 		make(map[rune]TokenID),
 		make(map[TokenID]rune),
 		make([]rule, nRules),
+		make(map[TokenIDPair]int),
 		make(map[TokenID]EncodedString),
 		make(map[string]TokenID),
 		specialTokens{-1, -1, -1, -1},
 		0,
 	}
 }
 
+func newTokenIDPair(left, right TokenID) TokenIDPair {
+	return (TokenIDPair(left) << 32) + TokenIDPair(right)
+}
+
 // DecodeToken converts the sequence of chars' ids into the string -
 // sequence of the corresponding chars
 func DecodeToken(token EncodedString, id2char map[TokenID]rune) (string, error) {
@@ -167,7 +184,6 @@ func ReadModel(reader io.Reader) (*Model, error) {
 		if err != nil {
 			return model, err
 		}
-		model.rules[i] = rule
 		if _, ok := model.recipe[rule.left]; !ok {
 			logrus.Errorf("%d: token id not described before", rule.left)
 			return model, errors.New("token id is impossible")
@@ -176,6 +192,8 @@ func ReadModel(reader io.Reader) (*Model, error) {
 			logrus.Errorf("%d: token id not described before", rule.right)
 			return model, errors.New("token id is impossible")
 		}
+		model.rules[i] = rule
+		model.rule2id[newTokenIDPair(rule.left, rule.right)] = i
 		model.recipe[rule.result] = append(model.recipe[rule.left], model.recipe[rule.right]...)
 		resultString, err := DecodeToken(model.recipe[rule.result], model.id2char)
 		if err != nil {
@@ -194,6 +212,10 @@ func ReadModel(reader io.Reader) (*Model, error) {
 		return model, err
 	}
 	model.specialTokens = specials
+	model.revRecipe[bosToken] = TokenID(specials.bos)
+	model.revRecipe[eosToken] = TokenID(specials.eos)
+	model.revRecipe[unkToken] = TokenID(specials.unk)
+	model.revRecipe[padToken] = TokenID(specials.pad)
 	return model, err
 }
 
@@ -287,3 +309,182 @@ func (m Model) DecodeFromStream(reader io.Reader) ([]string, error) {
 	}
 	return sentences, nil
 }
+
+type encodingToken struct {
+	id   TokenID
+	prev int
+	next int
+}
+
+type mergeEvent struct {
+	priority int
+	pos      int
+}
+
+type mergeQueue []*mergeEvent
+
+func (mq mergeQueue) Len() int { return len(mq) }
+
+func (mq mergeQueue) Less(i, j int) bool {
+	return mq[i].priority < mq[j].priority ||
+		mq[i].priority == mq[j].priority && mq[i].pos < mq[j].pos
+}
+
+func (mq mergeQueue) Swap(i, j int) {
+	mq[i], mq[j] = mq[j], mq[i]
+}
+
+func (mq *mergeQueue) Push(x interface{}) {
+	*mq = append(*mq, x.(*mergeEvent))
+}
+
+func (mq *mergeQueue) Pop() interface{} {
+	old := *mq
+	n := len(old)
+	item := old[n-1]
+	old[n-1] = nil // avoid memory leak
+	*mq = old[0 : n-1]
+	return item
+}
+
+// EncodeSentence takes a string of space-separated words and tokenizes each word
+// according to the BPE rules. Through encodingConfig one can state whether to add BOS, EOS tokens
+// and whether to reverse the output sequences. EncodeSentence returns the numerical encoding
+// of the sentence.
+func (m Model) EncodeSentence(sentence string, encodingConfig EncodingConfig,
+) (EncodedString, error) {
+	var encodedSentence EncodedString
+
+	if encodingConfig.bos {
+		if m.specialTokens.bos == -1 {
+			logrus.Error("Cannot use bos - model was trained without it")
+			return encodedSentence, errors.New("model was trained withous bos")
+		}
+		encodedSentence = append(encodedSentence, TokenID(m.specialTokens.bos))
+	}
+	for _, word := range strings.Fields(sentence) {
+		if len(word) == 0 {
+			continue
+		}
+		var encodedWord = []encodingToken{{m.spaceID, -1, 1}}
+		var pendingMerges mergeQueue
+		// Check whether two consecutive tokens can be merged and if so add merge suggestion to
+		// the priority queue
+		pushIfRuleExists := func(leftPos int) {
+			rightPos := encodedWord[leftPos].next
+			ruleCandidate := newTokenIDPair(encodedWord[leftPos].id, encodedWord[rightPos].id)
+			if priority, ok := m.rule2id[ruleCandidate]; ok {
+				heap.Push(&pendingMerges, &mergeEvent{priority, leftPos})
+			}
+		}
+		// Build linked list corresponding to the word's split on known chars and unknown tokens
+		unknownToken := false
+		for _, char := range word {
+			if charID, ok := m.char2id[char]; ok {
+				if unknownToken {
+					encodedWord = append(encodedWord,
+						encodingToken{TokenID(m.specialTokens.unk), len(encodedWord) - 1,
+							len(encodedWord) + 1})
+					unknownToken = false
+				}
+				encodedWord = append(encodedWord,
+					encodingToken{charID, len(encodedWord) - 1, len(encodedWord) + 1})
+				pushIfRuleExists(len(encodedWord) - 2)
+			} else {
+				unknownToken = true
+			}
+		}
+		if unknownToken {
+			encodedWord = append(encodedWord,
+				encodingToken{TokenID(m.specialTokens.unk), len(encodedWord) - 1,
+					len(encodedWord) + 1})
+		}
+		encodedWord[len(encodedWord)-1].next = -1
+		// Perform merges of subword tokens in the word according to the BPE model rules
+		for len(pendingMerges) > 0 {
+			event := heap.Pop(&pendingMerges).(*mergeEvent)
+			proposedRule := m.rules[event.priority]
+			leftPos := event.pos
+			leftToken := encodedWord[leftPos]
+			rightPos := leftToken.next
+			if rightPos == -1 {
+				continue
+			}
+			rightToken := encodedWord[rightPos]
+			// Check that the tokens suggested for the merge have not changed
+			if proposedRule.left != leftToken.id || proposedRule.right != rightToken.id {
+				continue
+			}
+			// Create token as a merge of the right and the left ones
+			leftToken.next = rightToken.next
+			leftToken.id = proposedRule.result
+			// Put merged token on the place of the left token
+			encodedWord[leftPos] = leftToken
+			// Put 'empty' token on the place of the right token
+			encodedWord[rightPos] = encodingToken{0, -1, -1}
+			// Add suggestions for merges for the new merged token
+			if rightToken.next != -1 {
+				encodedWord[rightToken.next].prev = leftPos
+				pushIfRuleExists(leftPos)
+			}
+			if leftToken.prev != -1 {
+				pushIfRuleExists(leftToken.prev)
+			}
+		}
+		// Retrieve all tokens that are left and append them to the result for the whole sentence
+		for pos := 0; pos > -1; {
+			encodedSentence = append(encodedSentence, encodedWord[pos].id)
+			pos = encodedWord[pos].next
+		}
+	}
+	if encodingConfig.eos {
+		if m.specialTokens.eos == -1 {
+			logrus.Error("Cannot use eos - model was trained without it")
+			return encodedSentence, errors.New("model was trained withous eos")
+		}
+		encodedSentence = append(encodedSentence, TokenID(m.specialTokens.eos))
+	}
+	if encodingConfig.reverse {
+		for i := 0; i < len(encodedSentence)/2; i++ {
+			encodedSentence[i], encodedSentence[len(encodedSentence)-i-1] =
+				encodedSentence[len(encodedSentence)-i-1], encodedSentence[i]
+		}
+	}
+	return encodedSentence, nil
+}
+
+// EncodeSentences takes a sequence of strings which consist of space-separated words and tokenizes
+// each word according to the BPE rules. Through encodingConfig one can state whether to add BOS
+// and EOS tokens (beginning and end of sentence) and whether to reverse the output sequences.
+// EncodeSentences returns the numerical encodings of the sentences.
+func (m Model) EncodeSentences(sentences []string, encodingConfig EncodingConfig) ([]EncodedString,
+	error) {
+	encodedSentence := make([]EncodedString, len(sentences))
+	for i, sentence := range sentences {
+		sentenceIds, err := m.EncodeSentence(sentence, encodingConfig)
+		if err != nil {
+			return encodedSentence, err
+		}
+		encodedSentence[i] = sentenceIds
+	}
+	return encodedSentence, nil
+}
+
+// EncodeStream reads a sequence of strings which consist of space-separated words from the given
+// stream and tokenizes each word according to the BPE rules. Through encodingConfig one can state
+// whether to add BOS and EOS tokens (beginning and end of sentence) and whether to reverse the
+// output sequences. EncodeStream returns the numerical encodings of the sentences.
+func (m Model) EncodeStream(reader io.Reader, encodingConfig EncodingConfig) ([]EncodedString,
+	error) {
+	scanner := bufio.NewScanner(reader)
+	var encodedSentence []EncodedString
+	for scanner.Scan() {
+		sentenceIds, err := m.EncodeSentence(scanner.Text(), encodingConfig)
+		if err != nil {
+			return encodedSentence, err
+		}
+		encodedSentence = append(encodedSentence, sentenceIds)
+	}
+	err := scanner.Err()
+	return encodedSentence, err
+}